# Any reason not to use distilled water to replace evaporation?



## NatalieT (Mar 20, 2007)

Is there any reason not to use distilled water to top up my tank (replace the water that evaporates)? I mean, is it usually full of chlorine, or does it have toxic chemicals leaching from the plastic jugs, or anything like that?

I know the distilled water shouldn't have any dissolved minerals, but that's exactly why I want to use it. My tap water is 25-50 ppm total hardness, but the water in the aquarium is between 120 and 250 ppm. (It's been about 2 years since I last tested it.) I assume this hard water is because the tank has been having a lot of evaporation (dry weather, and the tank has a screen cover which allows lots of air circulation). Every time I add tap water, it adds more minerals. It seems that the obvious way to fix this is to top up with distilled water, and let the plants gradually use the minerals until it reaches a reasonable level, then go back to using tap water.

I find it interesting that the pH has apparently risen with the hardness--it's about 6.4 in the tap water, but 8.4 or more in the tank. Since the fish and plants look OK, I'm not going to mess with that right now, but I will watch to see if it goes down again when I get the hardness down.


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## ashappard (Jun 3, 2006)

distilled water should have nothing good or bad in it.
pure stuff, and it would be good for top-off.

the pH could be rising over time because you are either dosing carbonates, or are adding them when you top-off with tap water.
other stuff could also be contributing. Substrate or rocks leaching minerals?


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## NatalieT (Mar 20, 2007)

ashappard said:


> distilled water should have nothing good or bad in it.
> pure stuff, and it would be good for top-off.


I thought so, but I also know that it's sold for human consumption--which proves nothing about fish safety!



ashappard said:


> the pH could be rising over time because you are either dosing carbonates, or are adding them when you top-off with tap water. other stuff could also be contributing. Substrate or rocks leaching minerals?


I'm not dosing anything (just adding fish food daily and water as needed.) I don't think it's the substrate, since I've got two tanks doing the same thing--one has typical inert "fish tank" gravel plus some traction sand, the other has dirt, traction sand, and "fish tank" gravel (layered in that order--the gravel is the top inch or so.) I think I trust the gravel from the fish store not to change the pH, and the dirt is far enough under it's unlikely to be affecting the water. I could suspect the sand, but it's only exposed in one tank and well buried in the other, so I don't think that's doing it either.

Anyway, as I said in the first post, I'm going to gradually deal with the hardness, and just watch the pH to see what it does. Right now I think stable pH is probably better than messing with it trying for "perfect" pH.


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## ashappard (Jun 3, 2006)

yes, stability always trumps a number


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## dwalstad (Apr 14, 2006)

NatalieT said:


> My tap water is 25-50 ppm total hardness, but the water in the aquarium is between 120 and 250 ppm.
> I find it interesting that the pH has apparently risen with the hardness--it's about 6.4 in the tap water, but 8.4 or more in the tank.


There's nothing wrong with distilled water except the cost.

Since your tapwater is very soft, you could soften the water simply by doing a few water changes. If your tank contains 250 ppm and your tapwater contains 50 ppm, a 50% water change would bring it down to 150 without spending a dime. A second 50% water change would bring it down to 100 ppm.

The high pH may be due to plant photosynthesis and bacterial processes. When reporting pH, it helps if you would specify which time of day. (It may be much lower in the early morning before plants start photosynthesizing and driving it up.)


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## NatalieT (Mar 20, 2007)

dwalstad said:


> There's nothing wrong with distilled water except the cost.
> 
> Since your tapwater is very soft, you could soften the water simply by doing a few water changes. If your tank contains 250 ppm and your tapwater contains 50 ppm, a 50% water change would bring it down to 150 without spending a dime. A second 50% water change would bring it down to 100 ppm.


Up until now, my policy was "no water changes--ever!" The reason is the copper content of the water--it kills fish (as I found out when I first set up my tanks!) I eventually figured out the problem and got some Seachem Cuprisorb to de-copper the tanks. Now keep the little packet of cuprisorb sitting in a bucket of water I use to top up the tank. I don't know how fast it really works, but I don't have any trouble if I let a 1 gallon container sit that way for 2 days before using it. The problem with that is that right now, I have a gallon of evaporation almost that fast! (two open-topped 20 gallon long tanks.) This would make it difficult to get enough water to "change" any. For now, I decided to spend a few bucks on some gallons of distilled water and use them to top up for a while, then test again and see how it's doing. Meanwhile, I may try dropping the cuprisorb into a larger container of water and see if I can get enough to actually change out some of the water, which I agree would be the obvious solution if it weren't for the pesky copper.



dwalstad said:


> The high pH may be due to plant photosynthesis and bacterial processes. When reporting pH, it helps if you would specify which time of day. (It may be much lower in the early morning before plants start photosynthesizing and driving it up.)


The 8.4 reading was from water taken in the "morning"--meaning sometime after the lights went on, but within the first 4 hours of light. I'm sorry I can't be more precise.


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## Perianth (Mar 17, 2009)

I’ve been trying to sort out a similar predicament, rapid evaporation even though my tanks are covered with custom made glass tops. I had these made at a local glass shop. In one tank, I’m trying to promote aerial growth, so it’s not completely covered. I’ve used the tap water purifier sold online to make up replacement water with good results. We have high KH around here. I suppose all these problems are the price we pay to have a lovely hobby.


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## dwalstad (Apr 14, 2006)

NatalieT said:


> Now keep the little packet of cuprisorb sitting in a bucket of water I use to top up the tank. I don't know how fast it really works,.


Thanks for info. Glad you found out what your problem was. I also have metal toxicity problem, only with zinc.

I use Tetra's AquaSafe. I just pour the recommended amount into the tank as I pour tapwater into the tank. Or I'll mix it up in a 1 gal container as I add tapwater. Since its a solution, its easy.

Planted tanks contain lots of DOC (dissolved organic carbon) that will chelate heavy metals like copper and zinc. So if I just do a minor water change, there's no problem. It's when I do a massive water change or set up a tank with 100% new tapwater that I'll get problems (killed plants and invertebrates, no hatching of brineshrimp eggs, etc).

Aquarium Water Conditioners that neutralize heavy metals (like Tetra's AquaSafe) behave like DOC. They neutralize heavy metals by chelating (binding) them. This is an almost instantaneous chemical reaction. The metal chelator EDTA does the same thing.

See my book, pp 9-19 for more information about metal toxicity.


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