Fluctuating water levels in my sump - I have a few theories...

[RodeoClownfish]

Hey guys, newbie here. Just started my tank this weekend. Current parameters and specs for my tank can be found in my profile. When I first filled the tank, I filled it to the water levels needed for the 75G tank and sump per the written "water level" mark on the sump. After running for the last three days, the levels fluctuate greatly. See pics for reference. I have a few theories as to why and was hoping someone here could confirm:

1) Theory one: I'm currently cycling my tank and dosing Brightwell QuickCycl (ammonia additive for a fishless cycle dosed to 3ppm) and MicroBacter7 at 15ml/day per the instructions. Is it possible that with the cycle and subsequent bacterial growth from the MB7 that the viscosity of the saltwater has changed and is resulting in a more viscous fluid, making the pump work harder and dropping the levels in the sump?
2) Theory two: barometric/atmospheric pressure - I noticed levels drop in the evenings and rise back up in the morning. Is it possible that pressure changes affect the ability of the pump and therefore affect the sump water level?

This is not affecting the performance of the tank, sump or return pump at all. Just curious as to why it's happening and if it's normal.

Here's a few pics for reference:
- Black line is early morning (not shown)
- Just below blackline is before noon
- "Water level" is after noon but before evenings
- below "water level" mark is after 6PM

Any help is greatly appreciated. Thank you.

 

[KrisReef]

Evaporation?

 

[WheatToast]

Have you been performing regular freshwater (RODI) topoff? I doubt what you mentioned in your theories will affect the water level too much, but the high circulation in our marine tanks means a great deal of our tank water evaporates, leaving saltier water behind. If this continues, the increasing salinity will harm your livestock.

 

[Chrisv.]

+1 for evaporation

 

[RodeoClownfish]

Have you been performing regular freshwater topoff? I doubt what you mentioned in your theories will affect the water level too much, but the high circulation in our marine tanks means a great deal of our tank water evaporates, leaving saltier water behind. If this continues, the increasing salinity will harm your livestock.

So you're on to something here, and if it weren't for the tight fitting glass lids on my display tank, I'd agree that is a source of water loss and increased salinity. However, I doubt that I've lost too much over the last 3 days with the glass lids. Salinity is still holding at 1.025 SG and I'm testing daily. If that *increases* (edited, my bad) I'll be sure to compensate with fresh RO/DI water.

 

[Chrisv.]

+1 for evaporation a second time

 

[RodeoClownfish]

Have you been performing regular freshwater (RODI) topoff? I doubt what you mentioned in your theories will affect the water level too much, but the high circulation in our marine tanks means a great deal of our tank water evaporates, leaving saltier water behind. If this continues, the increasing salinity will harm your livestock.

So maybe I'm thinking about this wrong @WheatToast . How much water can I expect to lose in a 3 day period? It may be more than I anticipated admittedly. Again, new here. The display has tight fitting glass lids but the sump doesn't, so evap could be happening in the sump, right? Is there a way to calculate how much water I lose in a day? I hadn't thought about evaporation from the sump.

 

[WheatToast]

So maybe I'm thinking about this wrong @WheatToast . How much water can I expect to lose in a 3 day period? It may be more than I anticipated admittedly. Again, new here. The display has tight fitting glass lids but the sump doesn't, so evap could be happening in the sump, right? Is there a way to calculate how much water I lose in a day? I hadn't thought about evaporation from the sump.

Not sure, but I am probably using about half a gallon on my high-flow system (40 gallon DT with half filled 20 gallon sump, all without lids) daily.

 

[mdb_talon]

So maybe I'm thinking about this wrong @WheatToast . How much water can I expect to lose in a 3 day period? It may be more than I anticipated admittedly. Again, new here. The display has tight fitting glass lids but the sump doesn't, so evap could be happening in the sump, right? Is there a way to calculate how much water I lose in a day? I hadn't thought about evaporation from the sump.

Ironically you already calculated and documented how much...with those pictures. If you dont have a leak....that fluctuation is evap

 

[RodeoClownfish]

Not sure, but I am probably using about half a gallon on my high-flow system (40 gallon DT with half filled 20 gallon sump, all without lids) daily.

Ok, then I need to be thinking about how to replenish the evaporated water in a 75 gallon display tank and 15 gallon sump. An automated top off tank would be really nice. May have to look into that. How do you determine how much RO/DI to add after a day? Do you have a specific level you measure to or do you work off salinity?

 

[RodeoClownfish]

Ironically you already calculated and documented how much...with those pictures. If you dont have a leak....that fluctuation is evap

@mdb_talon you're right. I'm just glad I'm paying attention I guess. So would you recommend filling the sump to the "water level" tag on the sump daily?

 

[mdb_talon]

Ok, then I need to be thinking about how to replenish the evaporated water in a 75 gallon display tank and 15 gallon sump. An automated top off tank would be really nice. May have to look into that. How do you determine how much RO/DI to add after a day? Do you have a specific level you measure to or do you work off salinity?

If it an ato you dont do calculations it does it automatically. If manual then you fill to "water level" line daily. If you remove water from the tank for some reason(ie dipping coral, etc) then you have to be a bit more careful.

 

[RodeoClownfish]

If it an ato you dont do calculations it does it automatically. If manual that you fill to "water level" line daily. If you remove water from the tank for some reason(ie dipping coral, etc) then you have to be a bit more careful.

@mdb_talon that is incredibly helpful. Thank you. I will be manually filling for now. This makes a heck of a lot more sense. Really didn't think I'd be losing that much to evap but I made it way more complicated than it needed to be. I'll just fill to the water level line daily.

 

[mdb_talon]

@mdb_talon that is incredibly helpful. Thank you. I will be manually filling for now. This makes a heck of a lot more sense. Really didn't think I'd be losing that much to evap but I made it way more complicated than it needed to be. I'll just fill to the water level line daily.

Yup it is one of those things that is obvious once you been in hobby awhile, but understandable that when new the evaporation can catch you by surprise. It often is more than expected. It can also fluctuate a lot if the humidity/temp/airflow in your house changes.

 

[RodeoClownfish]

Yup it is one of those things that is obvious once you been in hobby awhile, but understandable that when new the evaporation can catch you by surprise. It often is more than expected. It can also fluctuate a lot if the humidity/temp/airflow in your house changes.

@mdb_talon that's why I'm glad I joined R2R. Wouldn't have known otherwise. Seems obvious for seasoned reefers but for me this is all brand new. Again, thank you.

 

[WheatToast]

Do you have a specific level you measure to or do you work off salinity?

Both. I maintain the level I started off with when I set up the tank and test to make sure everything is in check.

Yup it is one of those things that is obvious once you been in hobby awhile, but understandable that when new the evaporation can catch you by surprise. It often is more than expected. It can also fluctuate a lot if the humidity/temp/airflow in your house changes.

Second! It definitely caught me by surprise two years back!

 

[melonheadorion]

on a 20 gal long tank, over the course of 3 days, i would probably see up to a full inch of water evap'd. on a sump, with the return chamber being considerably smaller, it surprises me more that you arent missing more water over 3 days

 

[RodeoClownfish]

on a 20 gal long tank, over the course of 3 days, i would probably see up to a full inch of water evap'd. on a sump, with the return chamber being considerably smaller, it surprises me more that you arent missing more water over 3 days

@melonheadorion admittedly, I was adding freshly mixed saltwater over the last few days (and removing it, now I know that was a problem) to try and get my levels right. I thought with the glass lids on the display that evaporation would be at a minimum. Since posting this I found significant condensation above the sump, which corroborates the evaporation issue. Moving forward I’ll be investing in an ATO. Had no idea that I’d lose that much to evap over the course of 3 days but now I know!

 

[RodeoClownfish]

And by adding I mean small amounts. Maybe a few cups, and any I took out was discarded.

 

[melonheadorion]

@melonheadorion admittedly, I was adding freshly mixed saltwater over the last few days (and removing it, now I know that was a problem) to try and get my levels right. I thought with the glass lids on the display that evaporation would be at a minimum. Since posting this I found significant condensation above the sump, which corroborates the evaporation issue. Moving forward I’ll be investing in an ATO. Had no idea that I’d lose that much to evap over the course of 3 days but now I know

this is my thinking behind how it all works. in my mind it does anyway.
with a sump setup, your DT level shouldnt actually change. the level that will change will happen in the sump. this would be because the return pump will pump water to the DT to the point that the overflow can only keep up with. the only way the DT level would change is if the drain or the return is working harder than what the other can add/remove, but that change in level would be minimal. the tank will drain from the overflow at a certain level and cannot be overfilled unless the return pump is working more than it can drain, which would make the tank overflow. in this case, for the DT to have a lower level, that would mean that the DT would have to remove more water than the return pump can put in it, which would be impossible since the overflow would stop draining water whent he water level gets below a certain point, and the only way for that to happen were to be if the return pump wasnt working,
so, with a sump setup, the only water level that you will have to replenish, assuming everything is setup and stays at constant rates, would be the level in the return chamber of your sump.

its just a matter of checking your water levels every day, and filling up what is missing while you do the ATO route. i personally just manually add water to my sump.