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How much water should evap from my tank per day? I feel like it is evaporating more than it should. I don't have an auto top-off system yet.


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How much water evaporates depends on the difference between your water temp and your room temp, the humidity levels in the air, the surface area of your tank, the amount of water movement/flow, whether your tank has a lid, whether you're using fans, and a host of other things.

For what it's worth, I have to top off at least 6 or 7 gallons per week (often more) in my 150 gallon tank, but that might be more or less than you depending on how we differ on all the variables noted above.


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I'm not exactly sure how many gallons - I was loosing a couple inches+ per day in my sump with an open top. I recently went back to glass to troubleshoot a different problem and it's around an inch now. If I top off every day to every second day it keeps everyone happy - I don't let it go longer than that though. 55g DT 10g sump.


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I have a smaller tank than you do (29 gallon), but I lose about 3 gallons a week to evaporation.


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I agree with other posters it is different from tank to tank. My 90 display with 30 sump would go through five to eight gallons a week during the summer with my ac cranking. During the winter would lose onky about three to five a week. If I placed glass tops on the tank it woukd decrease even more.


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I've got a 75 with a 40b sump, and I add 2.5 -3 gallons a day. My temp goes from 78 to 81 when the mh's are on. I have one fan in the canopy that runs 24/7.

T Smith

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2 gallons per day on my 100 with 55 sump, actual water volume about 120 gallons. I noticed that without the fan in the hood running it's about half that.


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Make a mark on the correct water level with a sharpie on your tank if you don't have a sump or if you do have a sump, make the mark on the sump.

Then fill up to the mark with RO, every day or every other day.

Dr. Reef

Dr. Reef at ur service
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my tank is IN-Wall with the tank being in the garage. in summer time it evap. over 5 gals per day. couldnd afford to live without an ATO
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