Water Evaporation In Tanks

[metulburr]

Is it normal to have a lot of water evaporation? I have a 30 gallon tank as well as a 5 gallon tank. I change out 30% of the water once a month.
 
By the end of the month in the 5 gallon tank, 20% of water is already gone due to evaporation. I take out 10% more and fill it to complete my water change. And the 30 gallon tank maybe a 2-3 gallons are evaporated. A good inch or two down. 
 
Is this normal? Do you guys repetitively fill this water to keep it topped off, or do you just fill it back up when you change out the water? IS there any harm in doing the latter? 

 

[Chad]

Yes, it's quite normal.
My 210 gallon tank evaporated at least a gallon a day, more in the summer. 
 
On my marine tanks I use an automatic top off system to replace the evaporation. This is vital in a marine tank as evaporation alters the salinity but in a FW tank it's not as important. But, it's quite normal and will be more or less depending on the size of tank, if there's a fan going, AC, time of year, climate, etc. So people with the same size tank may experience more or less evaporation than each other due to other environmental factors. 

 

[StevenF]

It's normal.  You can reduce the evaporation with a tight fitting cover.

 

[HarpyFishLover]

Mine used to not only evaporate but splash the sofa, because of a little open space where the filter goes. I fixed it by using stiff plastic packaging and cutting it to fit the hole. I call it my splash guard... it helps with evaporation, though.

 

[Byron]

Evaporation depends upon some factors: the water temperature, the tank being open or covered, and the ambient room temperature.
 
There is generally no problem with evaporation, but sometimes there can be, depending upon the water chemistry.  Water is a solvent, probably the strongest on this planet; this means it easily and readily absorbs substances as it falls as pure water (rain or snow) and percolates through rock, soil, etc.  When it evaporates from the aquarium, all of this dissolved substance is left behind.  This can cause issues; minerals, salt, etc will remain and accumulate.  Whereas a water change removes these with the water.
 
Which brings me to your water change...this should be more frequent, at least once a week minimum.  Aside from the above-mentioned, there are other substances in the water than will not be dealt with by filtration, only the water change.  A change of 30% every week will vastly improve the health of your fish (and plants if any).
 
Byron.

 

[Akasha72]

I'm inclined to agree that 30% once a month isn't enough (evaporation aside) Water changes remove Nitrates and hormones from the water. The more often you do this the better for the fishes health