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Re:High KH lowers pH?

    * From: "Hopkins, Samuel" <Samuel_Hopkins at marconi.com>

Someone on another one of my groups posted that if you add enough baking soda to water to raise the KH into the 100's the PH will stabilize either up or down at 8.4.

If you are talking about German degrees of hardness (dh), that much baking soda sounds absolutely lethal!

So for instance if you started with a PH of 9.5 and added enough baking soda to get your KH into the 100's your PH would drop to 8.4.

if you have any pH of 8 or greater, the way to get it down is to add CO2. Adding sodium bicarbonate adds the bicarbonate ion, which can lower the pH, but if your plants are utilizing the bicarbonate ion as a source of CO2, they leave behind hydroxide. You will wind up with sodium hydroxide. With certain aquatic plants and sunlight, you can get the pH up to eleven!. You would wind up with a tank based on water conditions of the Dead Sea. I think there are a few kinds of algae that can live there and a species of fly whose larva eats the algae. However, brine shrimp can't live there, and there are definitely no fish!

Anyone know if this is correct? I haven't gotten the chance to
test this.

Unless you have critters in your tank that really enjoy highly alkaline conditions, don't think of testing it. How are you getting water that tests higher than 8.4? Is that the pH of your tap water?

I can't see any real reason to ever add baking soda. If you have very soft, acidic water, you could add some baking soda to increase the capacity of the water to hold CO2, but I think it is better to add lime or ground limestone. This way you add calcium and magnesium bicarbonate, and you are adding two essential macronutrients rather than sodium, which plants don't need. Also, when plants are utilizing the bicarbonate ion from a solution of calcium bicarbonate, you get calcium carbonate, which precipitates out. when plants utilize the bicarbonate ion from sodium bicarbonate, you get sodium hydroxide, a strong base, which stays in solution. So, the pH goes up a lot more when plants are utilizing bicarbonate from sodium bicarbonate.

Paul Krombholz in steamy central Mississippi