Backyard Aquaponics
A place to discuss aquaponics

Yes.... algae will cause a diurnal swing in pH....

Actually, I just spoke to the manufacturer and as I mentioned previously, it is 94% KHCO3... but the other 6% is surfactants, ie detergents, which are apparently "safe for human consumption".
I was under the impression that detergents are bad news for fish.

Interesting. My understanding is that it is simply an organic fungicide. I used it for about 6 months in my first system without any problems.

I've heard of many people using eco rose so the surfactants must not be acutely toxic to fish in small amounts.
I've been buying potassium bicarbonate that is sold by beer/wine making supply places so it is food grade and doesn't contain any extra surfactants and I think it is actually cheaper.

For those of us chemistry challenged, here is the way I think of it.
The hydroxides raise the pH but they don't add buffering. So they are for use when you need to get the pH up in sort order but don't want to add lots of carbonates or buffer.

The carbonates and bi-carbonates are a bit weaker/slower acting but they are buffers or add hardness to the water. When you have too little or no carbonates or hardness in your water, the pH can drop rapidly and require constant adjustment. If there is too much carbonates or hardness in your water the pH will stay high.

For us in aquaponics, we want a little bit of hardness in our water so that the pH isn't too unstable but we don't want too much since the plants actually like a pH below 7 if possible (most hard water is going to be trying to stay either above 8 or at least above 7.6 until most of the carbonates are used up.)

So in aquaponics it can sometimes be a balance between making sure there is enough hardness to keep the pH from dropping too much all the time but also having the hardness low enough so we can manage to maintain a pH that is low enough to allow the plants good access to all the nutrients they need.

A carbonate hardness test kit is really easy to get and use. You probably want to make sure you add enough carbonate (calcium, magnesium and/or potassium) to get your carbonate hardness up at least between 20-40 ppm. Many people add carbonate hardness by hanging a stocking or mesh bag of chicken grit, limestone chips, shells etc in their tank. Doing it this way allows one to remove the bag when or if the hardness gets too high and to easily replenish the bag should the carbonates get used up.

My well water has over 170 ppm of hardness so I am working hard to collect enough rain water so that I can reduce the amount of hardness in my system and get better control of the water chemistry and pH.