Am I right in thinking that I have to be a little more careful with CO2 in my tank given I am using rainwater?
Presumably the low hardness means that co2 stopping and starting can cause larger ph changes?
And the low hardness in rainwater makes the ph swing for the ideal CO2 concentration larger?
Hello,
Its unclear whether you are using a pH controller or a simple uncontrolled injection, however we have to exercise caution when using CO2 regardless of whether rainwater or tap water is being used.
CO2 dissolves in tap water just as easily as in rainwater so the injection rate will be the same, however, as you mention, the pH excursions will differ between the two. This is one reason using a dropchecker can be useful in stabilizing the injection rate.
The important thing to remember is to not put the cart before the horse. CO2 kills fish but fish do not care about pH or pH swings.
The goal when using CO2 is to dissolve enough into the water to satisfy plants needs but not so much that the fish are poisoned.
That amount is the same regardless of the type of water.
The best thing to do is to first aim for a 1 pH unit drop from the natural pH of the water and monitor using the DC. If the DC shows only a dark green, for example, then this tells you that you can inject at a higher rate until the DC shows a light lime green. This will then tell you how much of a swing from it's natural pH that your rainwater will have.
Cheers,