[DJ88]

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If there is a lot of CO2, then alk is consumed and Ca stays the same.

Did you see what I quoted above? I'll post it again.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>FWIW, changes in CO2 only will have no impact on alkalinity (but of course huge ones on pH). So if you bubble CO2 into seawater, the alkalinity will remain unchanged (but the pH will drop). Likewise, if you somehow suck off all the CO2, the alkalinity will remain unchanged (but the pH will rise) Changes in alkalinity through the day would, IMO, reflect process involved in alkalinity addition (limewater etc.) and alkalinity consumption (e.g., calcification, parts of the nitrogen cycle, etc.).
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CO2 has no effect on Alk. This is from a chemist who does research with CO2 in solutions. Where are you reading that CO2 consumes Alk??? This is where I am really lost. It doesn't make any sense to me. Even without a chemistry degree I can see that CO2 has no effect on Alk. It does on pH as I see this daily with my pH monitor. I have measured my alk at many different times in the day and it never varies by any huge amount. pH does that is for sure. And I now know this is due to CO2 in the system.

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Is Bryosis calcium based ? If it is, then it will consume Ca and alk too

No it isn't.

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Also, you use an kalk reactor (and I don't). The kalk reactor will consume a lot of the acidity of the CO2. Hence, alk is maintain (never increased).

Stopped using it over a month ago till I build a new one. *anyone want a used nielsen reactor?* My Alk is still at 12. Measured it three times today to make sure. And CO2 isn't acidic. Once it interacts with the water it lowers the pH of the water.

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Also, my tank has three times the volume as yours but maybe 50% more water surface area. So, it will take longer for my tank to blow off CO2 (hence more alk consumption...if the CO2 does not get blown off).

With the larger waters surface to me you would get rid of excess CO2 faster than I would. The reason people have the effluent of a Ca reactor drip into a container is to increase the surface are of the effluent to release any excess CO2 in the effluent. As for Alk consumption I think you are a bit off in what happens in a system with regards to Alk CO2 Ph and Ca. I know you know the formulas and such. But I still say if you are having to add buffer to your system your Ca reactor is not dialed in correctly. To me it is as simple as that.

CO2 does not use up alk. that is what confuses me the most. I have posted two separate quotes by chemists to this fact.

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I haven't add Calcium to my system for a very long time. So I am either not consuming calcium (at all) or my reactor is working. So far, my SPS are growing and my coraline is spreading. So...it must be the reactor is working

Your Ca requirements in your 90 are quite minimal. It doesn't suprise me your reactor can keep up. But if the Alk is dropping(which is more important to keep track of in a system) your Ca reactor is not working. It doesn't get much more simple than that.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>If there is a lot of CO2, then alk is consumed and Ca stays the same. So, there are many things that can happen. If things aren't perfect, either Ca or alk will be consumed faster than the other. In my case, alk is falling a little bit faster (1 dKH over a month). Does that make sense ?
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nope. if your alk is dropping your Ca reactor isn't working. CO2 doesn't consume alk.