I think what's being meant about the pH of pure, or RO
, water is that yes... it *should* be 7.0 by definition, but for all practical purposes it's useless to measure since any slight shift in ion concentration will bugger up the results. Even with highly sensitive electronic stuff, any residue left on the probe, in the test tube, on the surface of the water... anything... can skew the results one way or another.
With regard to the question about shifting pH due to adding top off... thincat nailed it - you're replacing water that has evaporated with your top off. Everything that gives the water its specific pH value was left behind in the tank. So in effect, by adding top off, you're just putting the tank back to where it started from.
One thing about pH... pH will lower due to large amounts of biological activity. This is why the pH of a tank that's cycling will be lower than normal, and often bounce all over the place. There just a lot of biological stuff going on in there. Same if you overload a tank with fish. And same if you're battling algae or cyano
Just a hunch, but if you find your source of the cyano
/algae issue and get over that hurdle, your pH will probably come back up on its own. And adding stuff to raise your pH may be making the cyano
/algae issue worse, as Newfound77951 mentioned. You're kind of in a nasty loop, but maybe you're attacking the wrong end of the loop.
Yeah... your nitrates and phosphates are zero, but they normally are if you have a bad algae issue - the algae/cyano
is consuming the stuff as fast as it comes into the tank.
I know this doesn't answer your very original question about how to buffer a tank cheaper, but I have a feeling the wrong end of the dog is being chased in this case.