rohape

Well I am working on an ongoing issue with my KH constantly being 0 causing my pH to drop. I'm tired of always adding baking soda. I thought I had the solution when I found some "Calcium Sand" for terrariums. It is ground Calcium Carbonate. I googled it and found this interesting article on the wonderful Wikipedia. Seems that CaCo3 is not very soluble in water at all! Thats what I got from the article anyway. Here's the link if anyone is interested. It's a pretty neat read.
http://en.wikipedia.org/wiki/Calcium_carbonate

On the other side of my search "Calcium Bicarbonate". It seems there is no way to make this in a solid. This article is much shorter and again a very interesting read.
http://en.wikipedia.org/wiki/Calcium_bicarbonate

So my search continues on how to keep my KH and pH stable without adding baking soda every couple days. Any advice would be VERY welcomed!

Diana K

Test this in a bucket:
Coral sand is available in fish stores, it is commonly used in marine set ups.
I use it in Lake Tanganyikan, and brackish tanks. I also put a nylon stocking of it in the filter. (about half of a knee hi for a 45 gallon tank)

I use baking soda on water change day so the new water matches the established tank.

In tanks with Soil Master Select the KH and pH does drop, and it has taken over a year for the baking soda to make it stop. The KH used to reach 0 degrees within 2-3 days of a water change. pH was 6 to 6.2 (bottom of the test range) (I do not have coral sand in the filter of this tank)
Now the KH is about 2 a week or so after a water change (still about half the KH of the tap) and pH is around 6.5

I would think that coral sand in the filter would dissolve better when the pH is acidic (when you need it the most) and dissolve less when the water is closer to neutral. The reason for testing in a bucket, though, is that I do not know how much coral sand to use, and if it will work to target a particular pH.

dwalstad

[QUOTE=Diana K
I would think that coral sand in the filter would dissolve better when the pH is acidic (when you need it the most) .....[/QUOTE]

Good point. That is, when you need it most, it will be there.

Remember that KH and pH both influence each other. That is, acidity can lower KH by converting the bicarbonates into CO2 which goes off as gas and/or is taken up by plants. I'd want to make sure that the tank ecosystem isn't constantly generating acid (my book, pages 4 and 5). For example, nitrification is a strong acid-generating reaction that will certainly reduce both KH and pH. This could easily happen in softwater tanks where the fish and biological filtration outbalance plant growth.

If your tank has a normal GH (over 4) and zero KH, that would tell me that acidity might be the problem. That is, the tank is generating acid that dissolves the hardwater generators (CaCO3, CaHCO3, MgCO3, etc) just fine. This reaction inevitably releases Mg, Ca, and bicarbonates in similar proportions. The released Ca and Mg will stay in the water and increase the GH. BUT, the bicarbonates can be converted by acid to CO2 and lost from the tank (CO2 degassing and/or plant uptake of CO2).

I hope this makes sense.

Rohape, I couldn't get to your website, so unfortunatley, I don't have your tank specs. However, I'd like to know if your plants and fish are doing okay? It could be that plants are drawing down the pool of released bicarbonates and CO2 faster than you can measure the KH. If your plants are growing well, your fish are fine, and you are not artificially injecting CO2, a low KH in an NPT may not be a bad thing.

That said, I would make sure you've got a little bag of something in your filter (my book p. 87). Water hardeners and alkalinity sources can be coral sand, oyster grit, egg shells, crushed seashells, Tum tablets, etc. Try to crush these sources up a bit as the more pulverized they are, the faster they will dissolve.

rohape

Funny you wrote, I was just reading in your book about some of that process. P.93 and on.

When I first set up my tank I added crushed shell to my soil knowing my water wasn't very hard. I also added some later as the hardness went down. My GH is now probably off the scale for my dip testers. It reads at the highest level...180ppm I believe. The GH has been constant for the better part of a year. Only within the past couple months has my KH been dropping, along with my pH.

I've been reading a lot about this and have decided to take advice somewhere I read that fish can adjust to a gradual pH change. It's better to leave the pH stable, though it may be low, than to constantly attempt to repair and create pH fluctuations which will hurt the fish more.
I'm assuming that one culprit are my spiral val's. I have read that they are bicarbonate hogs.

As far as adding, in addition to the shell and now the calcium sand I added, I make my own "calcium cookies" from a recipe I got from applesnail.net. I posted this on the calcium stickie. I add these for my snails. In fact a lot of my hardness affinity is for my invertebrates.