Varying flow on return pump/overflow

[X-37B]

really good, simple idea. I'm gonna try this myself with my annoying red sea reefer.

Note it happens more on my rs170 than other systems. I was going to swap out the gate for a standard one but instead put a ball valve on the return. It now works as should and almost never has the issue. I still flush it every few months just to keep it clear.

 

[sgdnycct]

Before you change anything shut off your ato and open the drain valve 100%. I run 4 systems with gate valves, one is a red sea which has the worst valve.
My main system is 2 years old. Every so often water will go over the emergency and drain into the return. This tells me that there is some restriction in the overflow pipes. Could be algae, snails, or just buildup in the lines.
I call this the flush. Run it for several hours then reset it to proper flow. Works well and I run both ac and dc returns.
I have done the same over the years with standard ball valves too.

I’m going to try this. Thanks!

 

[sgdnycct]

Do you know which kit is the right one for the NYOS? I’m assuming the 300 and 440 are the same pipe sizes.

I believe they are -

Upgrade kit for REEFERs 32mm / 1” Down pipe​

Thank you!

 

[X-37B]

I’m going to try this. Thanks!

Let us know how it goes.

 

[sgdnycct]

really good, simple idea. I'm gonna try this myself with my annoying red sea reefer.

Note it happens more on my rs170 than other systems. I was going to swap out the gate for a standard one but instead put a ball valve on the return. It now works as should and almost never has the issue. I still flush it every few months just to keep it clear.

Interesting that you added a ball valve.

NYOS apparently used to ship with gate valves but switched to ball valves.

 

[sgdnycct]

Before you change anything shut off your ato and open the drain valve 100%. I run 4 systems with gate valves, one is a red sea which has the worst valve.
My main system is 2 years old. Every so often water will go over the emergency and drain into the return. This tells me that there is some restriction in the overflow pipes. Could be algae, snails, or just buildup in the lines.
I call this the flush. Run it for several hours then reset it to proper flow. Works well and I run both ac and dc returns.
I have done the same over the years with standard ball valves too.

I’m going to try this. Thanks!

I tried this out! I ran it for about 15 minutes. I turned the valve fully open and closed multiple times and I also cycled the pump intentionally catching air.

I won’t know for a few days if this helps but I did notice a lot of gunk coming out of first try return and then the pump. I kept cycling everything until the gunk stopped coming out. It must have been algae or biofilm. Whatever it was the fish and polyps ate it up!

I’ll monitor and update this thread.

Thanks everyone for your suggestions!

 

[sgdnycct]

So I’ve down the flush a few times. The first time I noticed a difference and reset everything. After the first time I no longer noticed a difference.

Unfortunately the problem continues. I did some more research and checked with @rtparty who has the same tank and is experiencing similar issues even with a pump upgrade to a Sicce.

I ran it through the AI and after some prompting it came up with the following. I’m goin to start look at each of these in turn and see what I find. Will update here.:

1. Evaporation and ATO cycling
This becomes a prime suspect. As water evaporates from the sump, the return chamber level drops, which changes pump intake conditions and slightly increases effective head. Then the ATO refills and flow picks back up.
This can show up as a repeating day/night pattern, especially if:
• evaporation increases when lights are on
• the return section is relatively small
• the ATO adds water in noticeable batches instead of tiny frequent corrections

2. Drain line behavior changing with air intake
If your overflow is running near the edge between siphon and mixed air/water flow, small changes in air entrainment can make the drain behave differently over time. That causes the overflow water height to drift even if the pump output is mostly steady.

Typical signs:
• occasional gurgling changes
• overflow box level slowly rising and falling
• system seems “perfect” for hours, then different later without you touching anything

3. Pump inconsistency or partial fouling
Even without the RFG, a DC return pump can still vary if:
• the impeller has film or debris on it
• the intake gets partially obstructed
• the controller is not holding speed perfectly
• the pump is sensitive to water level around the intake

4. Drain or overflow obstruction that comes and goes
Snail, shell fragment, macro, detritus, or biofilm can create minor restrictions that don’t fully block anything but still change system balance.

 

[rtparty]

My opinion after dealing with this for almost a year is that it’s a very poor design by NYOS between the ball valve and tiny overflow. If your overflow and return pump are even a few GPH off, the level changes so rapidly in their tiny overflow box it causes issues.

I really wish they made the box wider and made it a BeanAnimal setup as that would eliminate this issue. I don’t like running the tank super high so water trickles down the emergency pipe. They need a secondary drain right between the main and emergency

A gate valve would also help dial it in even more. The ball valve is not high quality IMO

 

[sgdnycct]

My opinion after dealing with this for almost a year is that it’s a very poor design by NYOS between the ball valve and tiny overflow. If your overflow and return pump are even a few GPH off, the level changes so rapidly in their tiny overflow box it causes issues.

I really wish they made the box wider and made it a BeanAnimal setup as that would eliminate this issue. I don’t like running the tank super high so water trickles down the emergency pipe. They need a secondary drain right between the main and emergency

A gate valve would also help dial it in even more. The ball valve is not high quality IMO

The small overflow being the issue is definitely possible’s some extra water in there would help minimize the fluctuation in water flows. Question is why/where/what is causing the flow change?

 

[sgdnycct]

Hi everyone!

Wanted to do a quick update. I’ve found so far that a small change in the water level of my return sumo chamber, as little as 1” affects the water level in the overflow.

I haven’t seen anything else affecting the water volume and was able to confirm by removing/ adding as little as half gallon of water to the sump.

I don’t remember the physics of pressure but I’m surprised such a small change affects the pump’s flow rate. My first thought was that the pump maybe is weak and unable to handle the variations but in this thread alone there were other pumps having similar issues.

Has anyone else who is having this problem noticed this as a potential source?

I’m going to keep testing stuff but this looks like the likely culprit. One thought for a solution is to get a better pump for my overflow that can cycle frequently so the volume doesn’t vary.

 

[sgdnycct]

Hi everyone, I wanted to update this thread with what I've found.

It took me a few days to stabilize the water levels at a few heights in my sump-mostly because the ball valve is a pain to adjust. Once I did get it set, I don't think it's any longer an issue.

I've confirmed the water level varying in the sump is my culprit. I set it at the highest water level I could ensuring the sump won't overflow if the pump shuts off. Doing this has stabilized the flow-going on 4 days now.

I don't know the math but it must be something to do with the water presser at the pump intake acting like head pressure. The higher the water lever (and pressure) the more water flows through the pump. What I also found is that the higher the level (pressure) the less sensitive it is to it. So, with the higher water volume in my pump chamber now (about 4 times the water volume from before I started this) it's become much more steady. I also upgraded my ATO pump and reduced the time it takes for the ATO to turn on.

I imagine it's some sort of inverse equation where the higher the water volume in the pump has an exponential effect of reducing effective head pressure. I might play around with trying to find an equation for it but I think for now and for my tank/sump I think I've figured it out. I'm glad I don't have to replace the ball valve for sure.

Thanks for all the suggestions! maybe this will help someone else. Also, as time goes by I'll update this thread with any other observations.

 

[Justfebreezeit]

Crazy how 1 inch of water level can affect head pressure enough to throw everything off. That just means the design of the system didn't allow for much wiggle room. Shame

 

[Freenow54]

HI all,

I've been dealing with this for a couple of months now. I set up my NYOS 440 in October 2025. Everything is doing great but I have this annoying thing going on with my return pump. It's a HYGGER DC3500 (925 GPH I estimate I'm getting half that with height and elbows at 100%). The NYOS came with a ball valve to adjust the drain flow rate. It's a pain but manageable. Here's what's happening:
1. I set everything up, clean pump, reconnect hoses, adjust the drain flow valve so my overflow is about 1" from the emergency overflow intake.
2. Everything works fine for a week or so then one day the volume in the overflow drops (or rises).
3. I readjust everything again. All is well for a few days then suddenly the water level in the tank goes up, pulling extra water from the ATO until it overflows into the emergency drain where is stabilizes. It's not a lot of water so it doesn't cause salinity changes.
4. I adjust again and increase the drain flow by opening the ball valve slightly. All is well for a while then after a few days the water level drops in my overflow so air is getting sucked into the sump.

The only variables I'm adjusting is the ball valve. I've tried cycling the pump to clear out any air that might be trapped. I've checked plumbing to make sure there aren't any blockages (which can't be this because the flow rate seems to go up or down).

Is there anything else I'm missing here? Some basic principle I'm forgetting? The power usage on the pump display is consistent.

Thanks in advance.

You mention hoses . I was warned away from that . Maybe you should hard pipe . I have never had an issue like that with my DC pump so that is why I suggest that . Unless you can find a spot where its sucking air

 

[Freenow54]

To make meaningful change here I think you need to embrace changing the valve type.

I had a redsea with that awful diaphragm valve, and I went through exactly what you're describing.

I since upgraded tanks to a waterbox 230.6 with a proper gate valve, and I rarely have to adjust.

Globe valves are far superior and that it is purposely designed for precise flow control

 

[TheDon]

Hi everyone, I wanted to update this thread with what I've found.

It took me a few days to stabilize the water levels at a few heights in my sump-mostly because the ball valve is a pain to adjust. Once I did get it set, I don't think it's any longer an issue.

I've confirmed the water level varying in the sump is my culprit. I set it at the highest water level I could ensuring the sump won't overflow if the pump shuts off. Doing this has stabilized the flow-going on 4 days now.

I don't know the math but it must be something to do with the water presser at the pump intake acting like head pressure. The higher the water lever (and pressure) the more water flows through the pump. What I also found is that the higher the level (pressure) the less sensitive it is to it. So, with the higher water volume in my pump chamber now (about 4 times the water volume from before I started this) it's become much more steady. I also upgraded my ATO pump and reduced the time it takes for the ATO to turn on.

I imagine it's some sort of inverse equation where the higher the water volume in the pump has an exponential effect of reducing effective head pressure. I might play around with trying to find an equation for it but I think for now and for my tank/sump I think I've figured it out. I'm glad I don't have to replace the ball valve for sure.

Thanks for all the suggestions! maybe this will help someone else. Also, as time goes by I'll update this thread with any other observations.

Hi, Can I ask what tank you have?

I have a reefer 250G3 and honestly I have fluctuations constantly! It can be fine for a day or 2 then it either goes way high or drops by an inch to 2 inches!

I did notice in the instructions that the adjustable baffle between skimmer and return pump should be set at 1cm from the top. Although this would mean the skimmer would have to be on a stand as water level would be too high in that section. My baffle is set all the way down and I still have the bubble trap sponge installed as I’ve been getting micro bubbles.

 

[sgdnycct]

I have the NYOS 440 with a ball valve.

Does yours have a gate or ball valve? This is the answer that most often comes up as the issue. I’m convinced it’s not a ball valve/gate valve problem. At least not in short term. Over extended periods one or the other could get clogged.

After all the testing and trials I did I figured it’s three fold issue:

1. Small adjustments in water height at the pump inlet make a big difference in the water level of the overflow box. 2. Problem here is the overflow box is too small-I think. Once it gets to a certain height then the water level of the tank may increase, causing huge swings in the sump water level. In my case I found ~1.5 gallons was the most. It’s not enough to affect water chemistry but it does alter the surface skimming or noise in the overflow.
3. I am starting to think a big part or likely the biggest is the pump varies flow slightly. I have a DC pump and I wonder, this being an older house, if slight voltage changes could affect the power levels of the pump.

When you take these things together I can see now my issues. I ended keeping the water level in the overflow on the low end. This causes some noise when the return flow drops but doesn’t stop surface skimming when it increases. It also sets a maximum water level change in the sump so I don’t have big fluctuations in ato water going in.

 

[TheDon]

I have the NYOS 440 with a ball valve.

Does yours have a gate or ball valve? This is the answer that most often comes up as the issue. I’m convinced it’s not a ball valve/gate valve problem. At least not in short term. Over extended periods one or the other could get clogged.

After all the testing and trials I did I figured it’s three fold issue:

1. Small adjustments in water height at the pump inlet make a big difference in the water level of the overflow box. 2. Problem here is the overflow box is too small-I think. Once it gets to a certain height then the water level of the tank may increase, causing huge swings in the sump water level. In my case I found ~1.5 gallons was the most. It’s not enough to affect water chemistry but it does alter the surface skimming or noise in the overflow.
3. I am starting to think a big part or likely the biggest is the pump varies flow slightly. I have a DC pump and I wonder, this being an older house, if slight voltage changes could affect the power levels of the pump.

When you take these things together I can see now my issues. I ended keeping the water level in the overflow on the low end. This causes some noise when the return flow drops but doesn’t stop surface skimming when it increases. It also sets a maximum water level change in the sump so I don’t have big fluctuations in ato water going in.

Mine is the new Red Sea Reefer G3 with the new gate valve! Constantly fluctuating and I’ve tried everything! Running with a new Red Sea ReefRun 4000g2 at 44%

 

[sgdnycct]

Wish I could give you some advice that works. We’re definitely not the only ones with this problem.

 

[Freenow54]

I have the NYOS 440 with a ball valve.

Does yours have a gate or ball valve? This is the answer that most often comes up as the issue. I’m convinced it’s not a ball valve/gate valve problem. At least not in short term. Over extended periods one or the other could get clogged.

After all the testing and trials I did I figured it’s three fold issue:

1. Small adjustments in water height at the pump inlet make a big difference in the water level of the overflow box. 2. Problem here is the overflow box is too small-I think. Once it gets to a certain height then the water level of the tank may increase, causing huge swings in the sump water level. In my case I found ~1.5 gallons was the most. It’s not enough to affect water chemistry but it does alter the surface skimming or noise in the overflow.
3. I am starting to think a big part or likely the biggest is the pump varies flow slightly. I have a DC pump and I wonder, this being an older house, if slight voltage changes could affect the power levels of the pump.

When you take these things together I can see now my issues. I ended keeping the water level in the overflow on the low end. This causes some noise when the return flow drops but doesn’t stop surface skimming when it increases. It also sets a maximum water level change in the sump so I don’t have big fluctuations in ato water going in.

Skimmers do not have either one . They have Globe valves . That is what the configuration of a Globe valve is . Not a ball or a disc ( wedge ) it has a rubber stop that is turned down on the opening just like the old two lever taps did . Exactly the same thing. They are more sensitive to adjustments which is why they were made . Even though the literature that comes with an Octo Skimmer calls it a gate it is wrong . I think They are purposely dumbing it down . Anyway the hieght of the skimmer is crucial so as not to have back pressure to me . A dc pump supply will not be effected by any slight voltage fluctuations . My system has worked the same for 8years . The discharge from the skimmer allows the water to clear the baffle slightly into the next chamber. I believe the noise and maybe the disruption is caused by your pipes supplying the sump. They should be close to the bottom. I did read that when shutting down the pump for maintenance on an overflow box causes an air lock. I can see that happening . The guys solution was to drill a small hole in the down elbow . Mine is under water and have never had an air lock. I am going to put a longer pipe on the down elbow to see . I did not glue that pipe

 

[sgdnycct]

I have the NYOS 440 with a ball valve.

Does yours have a gate or ball valve? This is the answer that most often comes up as the issue. I’m convinced it’s not a ball valve/gate valve problem. At least not in short term. Over extended periods one or the other could get clogged.

After all the testing and trials I did I figured it’s three fold issue:

1. Small adjustments in water height at the pump inlet make a big difference in the water level of the overflow box. 2. Problem here is the overflow box is too small-I think. Once it gets to a certain height then the water level of the tank may increase, causing huge swings in the sump water level. In my case I found ~1.5 gallons was the most. It’s not enough to affect water chemistry but it does alter the surface skimming or noise in the overflow.
3. I am starting to think a big part or likely the biggest is the pump varies flow slightly. I have a DC pump and I wonder, this being an older house, if slight voltage changes could affect the power levels of the pump.

When you take these things together I can see now my issues. I ended keeping the water level in the overflow on the low end. This causes some noise when the return flow drops but doesn’t stop surface skimming when it increases. It also sets a maximum water level change in the sump so I don’t have big fluctuations in ato water going in.

Skimmers do not have either one . They have Globe valves . That is what the configuration of a Globe valve is . Not a ball or a disc ( wedge ) it has a rubber stop that is turned down on the opening just like the old two lever taps did . Exactly the same thing. They are more sensitive to adjustments which is why they were made . Even though the literature that comes with an Octo Skimmer calls it a gate it is wrong . I think They are purposely dumbing it down . Anyway the hieght of the skimmer is crucial so as not to have back pressure to me . A dc pump supply will not be effected by any slight voltage fluctuations . My system has worked the same for 8years . The discharge from the skimmer allows the water to clear the baffle slightly into the next chamber. I believe the noise and maybe the disruption is caused by your pipes supplying the sump. They should be close to the bottom. I did read that when shutting down the pump for maintenance on an overflow box causes an air lock. I can see that happening . The guys solution was to drill a small hole in the down elbow . Mine is under water and have never had an air lock. I am going to put a longer pipe on the down elbow to see . I did not glue that pipe

Thanks for the information on the valve types.

We are referring to the main sump pump.