Sump water level won't stabilize

[Salty Rambler]

The water levels in my sump won't stabilize after water changes. It ran fine for circa a year, before I moved the tank long distance. Now that I have the tank running again, it is a struggle to keep the water levels balanced despite the presence of an ATO.

I have a DIY overflow (weir) plumbing. The overflow PVC pipe transitions to a hose to flow down to the first chamber of the sump, which contains a HOB skimmer. The end of the overflow hose is submerged below the water line in the first chamber of the sump. The return pump is in the last chamber and returns water to the opposite end of the tank from the overflow.

Any thoughts on whether my issue is related to the siphon?

The water continues to drain down the overflow weir and into the sump, and there is a ball valve to help regulate the flow of the return pump. There is no noise coming from the drain, and the siphon restarts when the return pump is turned back on, but multiple adjustments need to be made to the ball valve on the return pump to get the levels somewhat stable. The levels will stablize for half an hour or so, and then I'll come back an hour later and the water levels have moved up or down. The skimmer isn't working overtime, so I've likely ruled that out as a culprit.

If this is a siphon issue, would something like an aqualifter help fix it? If it isn't a siphon issue, could it be a faulty valve, an aging return pump (it used to restart immediately, but now it struggles for about five seconds before it kicks back on), or some other well known issue that I've overlooked?

 

[Mical]

It's hard to say without seeing your set up but I'm with the crowd that doesn't restrict the return to the sump. If I had to, I'd lean towards restricting the return pump. You have more control from the pump side vs the return side.

 

[Spieg]

Have tried unplugging the ATO to be sure it isn't malfunctioning? Does the water level in tank change at all or only in the sump? Is the return pump AC or DC/controllable? Some photos might help.

 

[vetteguy53081]

Sounds like return pump may be pumping the water out slightly faster than it is coming in
Try bringing outward flow down just a little and see if it compensates

 

[Salty Rambler]

Have tried unplugging the ATO to be sure it isn't malfunctioning? Does the water level in tank change at all or only in the sump? Is the return pump AC or DC/controllable? Some photos might help.

The ATO doesn't seem to be impacting it -- the levels are moving whether the ATO is plugged in or not. The tank level drops as the sump level rises and vice versa.

The odd part for me is that it will appear stable, I'll watch the levels for 30 minutes and it won't move, I'll think that I finally have it dialed in, and then I'll walk away to have lunch and when I return the levels have climbed or fallen significantly, i.e. more than regular evaporation, and continuing to move in a direction of either overflowing the sump or the DT.

The return pump is AC, so I've been controlling the flow with a ball valve on the return line to the tank, which I'm assuming may have put undue wear on the pump itself. I'll take some pictures when the lights are back on.

 

[Billdogg]

I would take a close look at the drain line/siphon. Consider replacing that entire part. You say it's DIY, so you'll only be out about $5 in PVC if replacing it doesn't help.

If you use your ATO with it fluctuating like that bad things will happen to your salinity and perhaps even cause a flood.

If it were mine, I'd figure out a way to make the switch to a tried and true drain system - a Durso, Herbie, or beananimal will serve you much better.

 

[threebuoys]

A couple of suggestions if you haven't already tried.

First, do not activate the ATO until you are sure the levels in both the tank and sump are stabilized. I would wait at least 6 hours if not longer.

Second, I prefer to not restrict the return flow to the tank with valves. This could put stress on the pump that may cause fluctuations in actual return flow. (An argument can be made that the effect of a partially closed return valve on the pump is no different than changing the height between the pump and the top of the display tank, I think the tuning is easier if either the overflow or the return flow is established before I start tuning.) I have the advantage of an infinitely adjustable DC return pump. Even so, a minute change in the rpm of the pump will have a significant impact on the return volume. Once I get a return flow I'm happy with, I try to do all water level adjustments using the valve controlling the flow to the sump.

Third, as I indicated adjust the flow to the sump, but in very minute amounts. Usually, I can hardly tell anything has changed until I let the system work for 15 - 30 minutes. It helps if you have a gate valve instead of a ball valve because very small adjustments are easier to control. That said, I actually have ball valves on mine.

Fourth, if you have air gurgling in the flow to the sump, you are not getting the full water flow the valve position would allow and if the air slowly purges from the line, water flow will increase. I find that sometimes if the water level is too low in the display tank, the air will not purge completely Other times, the shear force of the downflow will prevent the air bubbles from rising back to the tank, but the downward force is not strong enough to get the air to the sump. I expect you've experienced the same. It can be a real bugger to fine tune.

You may also want to turn off your skimmer and any reactors until after the levels are stable. When you turn it on, you'll probably notice a drop in water level in your sump, but probably not enough to alter the water flow.

Only after levels are stable, turn on the ATO.

If you still have problems, perhaps you have some debris or wear in the return pump that prevents it from delivering a constant flow rate.

 

[uninformed]

Start with the basics: fluctuating water levels in your sump are the result of unbalanced flows in and out of it. As you already said, the ATO won’t do that—the volume of water moving isn’t large enough—and the skimmer has nothing to do with it, since that is net zero flow (i.e. it’s all within the sump.

On your return, you have an AC pump, so flow is constant for a given position of your discharge valve, barring some other kind of intermittent blockage, like a malfunctioning check valve.

However, even in that scenario, a properly functioning drain would handle any variation of flow to the DT. Consider if you had an open trough as a drain; you could turn the return flow up or down as much as you wanted and all that water would return to the sump. I think you can see where this is going...

The problem is in your drain line. A couple questions:

• Do you have a single line draining to your sump?
• Is there any place in the drain line where you can accumulate air?
• How far under water is your drain line in your sump?

 

[Brett S]

So a couple of thoughts here. You don’t want to try to match your return pump rate to your overflow rate. You want to set the return pump to whatever flow you want and then match the the overflow to that rate. You’ll be driving yourself crazy if you’re trying to adjust two things.

However second and most importantly, do you have two (or three) drains or just one? You didn’t really specify, but it sounds like it’s just one. If that’s the case you should *never* restrict a single drain at all. You need to remove the valve on that drain and let it run wide open. Unfortunately it will be louder, but you won’t be risking a flood. As you discovered, if it isn’t tuned to exactly match your return pump flow (which is all but impossible to do) then it is very likely that you may pump too much water into your tank and cause a flood. Or an obstruction could end up in the drain which could plug it or partially plug it, which would also lead to a flood.

The reason herbie and bean animal drains work is because they have one drain that is run with a restriction at a full siphon and a second drain that allows a small trickle of water. This small trickle of water is the key. As you have discovered it is nearly impossible to get a full syphon drain to exactly match your return pump speed and small things can upset that balance, so by running one drain at a full syphon and a second drain at a trickle then that trickle will allow for some flow variance without affecting the water level in the tanks. Additionally, having that second or third drain provides a backup in case the full siphon drain does get restricted. Water can flow down the extra drain and there will be no flood.

So, I think this is probably not the answer you want to hear, but you really need to run your single drain unrestricted. (You can look into setting it up as a durso to try to keep it reasonably quiet) or you need to add a second or third drain and run them as a herbie or bean animal.

 

[Salty Rambler]

Start with the basics: fluctuating water levels in your sump are the result of unbalanced flows in and out of it. As you already said, the ATO won’t do that—the volume of water moving isn’t large enough—and the skimmer has nothing to do with it, since that is net zero flow (i.e. it’s all within the sump.

On your return, you have an AC pump, so flow is constant for a given position of your discharge valve, barring some other kind of intermittent blockage, like a malfunctioning check valve.

However, even in that scenario, a properly functioning drain would handle any variation of flow to the DT. Consider if you had an open trough as a drain; you could turn the return flow up or down as much as you wanted and all that water would return to the sump. I think you can see where this is going...

The problem is in your drain line. A couple questions:

• Do you have a single line draining to your sump?
• Is there any place in the drain line where you can accumulate air?
• How far under water is your drain line in your sump?

I have a single line. The line starts in a weir, but I'm sure at some point air could enter or perhaps not have been removed fully when the siphon started, which is why I'm wondering if an aqualifter should be my next step. The line ends two inches underwater in the sump.

After my first post, I broke the return and overflow down and stuck a HOB filter on temporarily, and gave the whole system a deep clean. When I reassembled it, I was able to finally get the levels to somewhat stabilize, but the DT levels aren't as high as I would like, and the system is draining any new water added to the DT down into the sump. I'm guessing that means I could tweak it so that the return pump was pushing more water into the DT, but for now, I'm enjoying the brief stability.

 

[Salty Rambler]

So a couple of thoughts here. You don’t want to try to match your return pump rate to your overflow rate. You want to set the return pump to whatever flow you want and then match the the overflow to that rate. You’ll be driving yourself crazy if you’re trying to adjust two things.

However second and most importantly, do you have two (or three) drains or just one? You didn’t really specify, but it sounds like it’s just one. If that’s the case you should *never* restrict a single drain at all. You need to remove the valve on that drain and let it run wide open. Unfortunately it will be louder, but you won’t be risking a flood. As you discovered, if it isn’t tuned to exactly match your return pump flow (which is all but impossible to do) then it is very likely that you may pump too much water into your tank and cause a flood. Or an obstruction could end up in the drain which could plug it or partially plug it, which would also lead to a flood.

The reason herbie and bean animal drains work is because they have one drain that is run with a restriction at a full siphon and a second drain that allows a small trickle of water. This small trickle of water is the key. As you have discovered it is nearly impossible to get a full syphon drain to exactly match your return pump speed and small things can upset that balance, so by running one drain at a full syphon and a second drain at a trickle then that trickle will allow for some flow variance without affecting the water level in the tanks. Additionally, having that second or third drain provides a backup in case the full siphon drain does get restricted. Water can flow down the extra drain and there will be no flood.

So, I think this is probably not the answer you want to hear, but you really need to run your single drain unrestricted. (You can look into setting it up as a durso to try to keep it reasonably quiet) or you need to add a second or third drain and run them as a herbie or bean animal.

I probably wasn't as clear in my initial description, but my restrictor is on the pump line, vice the overflow. The overflow drain doesn't have a restriction on it. I have just the one, but have been debating whether to add a second -- I attempted it a few months ago, but couldn't get the backup drain to maintain a siphon to keep trickling water. Either drain on its own would work fine, but I couldn't quite get two of them to function properly in tandem. I might get the second one out and try to run them both again.