Evaporation and water changes

[CieLaw]

So I have a question about water changes and evaporation for my 20 gallon tank.

So I have my tank covered with the black plastic hood that came in the Tetra 20g aquarium kit. I do have the heater sitting fairly low in the water, but instead of the tetra whisper filter I have a marineland penguin 150 bio wheel filter which is for up to 30g tanks. (I thought maybe this had something to do with my evaporation)

I have very consistent weekly evaporation, about 2 gallons per week...which I feel is a lot.

When I do water changes, am I supposed to refill then change 20-25% or change 20-25% of what is in tank and then refill? I feel like I'm losing and changing a lot of water, but I remain very consistent with my changes. Should I be adding water back into the tank throughout the week?

My fish don't seem bothered by the dropping water level throughout the week. They are happy and thriving.

What can I do to cut my evaporation? Or is that much normal?




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[rlederer]

Evaporation rates depend upon water temperature, humidity in the room, and movement of the water surface. A 10% loss per week seems a bit high, but not problematic. Now, when the water evaporates, the concentration of ammonia, nitrates, and nitrites goes up even though their absolute amounts don't change. As long as you keep your ammonia, etc levels reasonable, you don't have to add water during the week, but it's probably a good idea. And then do your changes as usual.

 

[Rosenweiss]

I have a 20g high with some evaporation and I fill it between water changes so the fish always have the most water to swim in. Will also help keep the nitrates from being as concentrated

 

[Chest Rockwell]

That is a lot of evaporation for a 20G! I usually add about 3G of water a week for my 90G with no covers. Water temp is around 78F and room temp ranges from 75.5-80.5F. Do you have the top fully covered? That should pretty much lower it to like a quarter gallon a week maybe less when adding. Do you have a light on a lot, that could burn up the evaporating water?

 

[enrgizerbunny]

I have glass covers on my 55. I just siphon out and refill to the top. Don't have to bother to fill then change, pretty much a waste of time to do that. Topping up with distilled or purified water between changes is good to go, though. Tap water is cautioned against because of distilled solids increasing.

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[ScotJudd]

You can buy a clear plastic evaporation tray to fit on the rim of your tank. This keeps the moist air away from the hot lights and the moisture condenses on the tray and drips back into the tank. You might not be able to get tray specifically for your tank but a little engineering could be used to adapt a standard tray. They can usually be cut with sharp scissors.
The down side is that the tray requires cleaning to ensure that the light level reaching the water doesn't decrease but the upside is less evaporation and the light bulbs remain clean.
It is a cheap solution and maybe worth a try.


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[IllusionX]

I'm without lids since we've started our 55G.

Temperature is changing here, and since last week, I add 2 to 3 quarts of water every day.

My 20G loses 1-2qt everyday.

 

[gilpi]

Evaporation is no problem, just replace whatever is needed.
My 40 gallon with 80 degree temp, loses about the same amount as yours, the 55 gallon tank I keep at 76 does not lose as much but then the 40 gallon has more area so I'm assuming that has something to do with the faster evaporation.
And yes, the bio wheel filter due to more water movement will contribute to faster evaporation.