# evaporation



## squidlips (Apr 26, 2009)

Hi 

Ive got a heavily planted , soil sub aqum. I dont do many water changes but because I cant have lids on my tank I get high evaporation and therefore I am regularly topping up the water level.

Will this cause my water to rise in GH , KH , salts/minerals given that these are left behind when water evaporates. Or will the plants use the things.

I suppose what I am asking is , what is the outcome of lots of evaporation and no water changes in a heavily planted tank.

Thanks 

Craig


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## Seattle_Aquarist (Mar 7, 2008)

Hi Craig,

It is not possible to know for sure unless you are doing tests, but it is doubtful the plants are using up the Mg, Ca, and other minerals as quickly as they are building up from the evaporation.

Eventually plant growth will suffer once conditions are beyond what the plants can adapt to. I would do 25% water changes once a week if no fertilzers are being added; 50% weekly if you are adding ferts.


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## mudboots (Jun 24, 2009)

If you are on city water you can sometimes find a report on the water sources and get a general idea of what's in your water, but it is vague at best. I agree with Seattle that occassional water changes are a good thing, though I don't normally do 25% a week. Lately I am doing so, but that's just to get tannins out of the water from a piece of driftwood I have. I usually go about a month or three and do about 40%.

But for what it's worth, the tanks always look a little healthier right after a water change. The reason I don't do them regularly is not because of water quality concerns, it's just because I don't want to until after about a month or three...


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## ItsDubC (Jan 12, 2008)

There are tanks out there that are many years old doing fine w/ just water top-ups. Minerals will definitely build up over time, but it seems that most ppl end up breaking down their tanks and starting anew for whatever reason before that build-up reaches problematic levels.


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## Diana K (Dec 20, 2007)

That happens in the summer in my tanks. I top off with tap water GH and KH of around 4-5 degrees, and maybe once a month water changes. This results in an increase in GH and KH over the summer and the TDS rises from roughly 300ppm to about double. 

It is reversed in the winter, when I use rain water as much as possible for changes and topping off. 

No, in a low tech set up (El Natural or similar) the plants do not use the minerals as fast as they can accumulate via evaporation followed by topping off with average tap water. Using a very soft water for topping off (RO or DI) will minimize the build up.


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## Oonagh (May 8, 2006)

That is good food for thought. What is TDS?


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## Tex Gal (Nov 1, 2007)

Total Dissolved Solids


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## Diana K (Dec 20, 2007)

TDS is a measure of all the stuff dissolved in the water. Minerals, salts... 

It is a quick way of assessing what is going on with the water. 
It does not tell you what each mineral is, though. Other tests will tell you that. A separate test for each thing you want to know. 

Once you have tested using all the tests you have for a while you will get a pretty good feel for what is going on, and simply testing the TDS will go a lot faster, and tell you how things are going. 
Especially when you are looking at exactly that: The overall accumulation of 'stuff' from evaporation. 

This does not mean you can or want to give up the individual tests. Your original question is entirely valid, and you do want to test and answer that. 
Each aquarium is different. It might be that the plants in your set up do indeed use up all the calcium and magnesium between water changes, so you might need to top off with tap water (assuming it has enough minerals) to replace what the plants use.


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