My 55g maintains 400 ppm cal and 2.5 kh alk with no additives. I do use crushed oyster shells in a diy filter box though and they did change it from 250-300 ca and 4 kh alk. so my alk did raise after the ca increase. perhaps that has happened to you also.
2.5Kh, are you having a laugh, thats lower than my Softwater Amazon tank (4 Dkh). you should be pullin at least 8, thats DkH
With no additives your Oyster shells would have been adding the only buffering in your system, Man, it even comes out of the tap at round here at 7DkH. Your lucky you had Oyster shell or id suspect a Ph crash for you.
Upon measuring my Ca and Alkalinity yesterday I got 4.2 and 420.
Ca looks good, Alkalinity is half of what it should be. I think I know how to fix it: add oly the alkalinity component of the two component additive, right? Do I need to worry about anything else (pH or other by-products since I don't add them in balance)?
Ok, chemistry 101. Ph is actually a total of your Gh and Kh, or General Hardness and Carbonate hardness. These in combination buffer the water and stabalise the Ph at a given level, in this case an alkaline solution rather than an acid (allthough your getting very close)
Your Kh will have a direct effect on the Ph, for example, a Dkh of about 4.0 will have a Ph of about 8. If you lower the Kh the Ph will also lower.
From my expirience the Gh has little or no affect on Ph.
I wouldn't waste your 2 part additive by only using one part of it, keep it for the dosing it suggests and get some Kent KH+, or just use baking soda. This way you wont end up with just one of the two parts left over.
Second question: what would make alkalinity go down (in time, say in 3 months) significantly lower than Ca? I have a DSB, can that supply the needed Ca replacing what my corraline algae are consuming? But shouldn't it also supply alkalinity? Stumped.
What would make the alkalinity go down, well that would be a process of either precipitation or use by all the stony corals/corraline algie you have growing.
And with the kind of levels you have it wouldn't take very much, the higher it is, the more buffering potential there is, the more it will need to shift it.
The Ca or calcium content is only supplied in your case when the Kh is used up, lowering the Ph to a point low enough to actually disolve the sand bed. This is good if it happens to be the inside of a calcium reactor, but bad if it happens to be in the system.
This could be why you have such a high calcium content but such a low Kh. Because your low Ph (a result of low Kh) is disolving the sand, raising calcium levels, while giving you a relatively low Kh. I would dread to think what your Ph is.
I dont see why the sand would supply you with Kh, maybee Gh but not Kh. Ca, or calcium yea, because its arragonite, but not Carbonate hardness, maybee a little general hardness.
I really dont understand why you would expect your sand to fullfill both your buffering and calcium requirements. Sounds to me like youve been listening to someone who doesn't actually have a clue what their talking about. I suggest you buy a book that explains all of this in full, as your information is dangerously incorrect, even your questions are a little arse about face.
Man youve even got me confused now.
The sand really should be there as a buffer, and a final one at that, a last resort to avoid a Ph crash. Instead you seem to be relying on the low Ph, Kh of your system to disolve the sand to raise Ca. You have basically turned your tank into a very slow calcium reactor.
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