[sphelps]

The way I see it is if you're pH is low at a natural alk level you've got other problems to address that aren't really solved by simply adding more carbonate to increase alkalinity. More than likely the amount of CO2 in the water is too high and instead of covering this issue with something else you should be looking at the source of the problem. 99% of the time it comes down to the calcium reactor for obvious reason, it runs on CO2. The problem is very few understand the science behind these reactors and simply set an internal or effluent pH and figure that's good. However there is much more to consider including media type, reactor design, effluent flow rate, circulation flow rate, and CO2 flow rate.

For example, you find your tank pH is lower than normal say 7.8. First off you know that tanks using a Ca reactor will usually have a little lower pH than tanks using other methods, but I don't think lower than 8.0 mid-day is normal. So what's the problem? Too much CO2? Most likely but what's the solution? Most would simply bump the alkalinity up by increasing the output of the reactor by increasing the CO2 input which will actually add even more CO2 to the tank. What you should do is adjust your reactor, you've obviously got too much dissolved CO2 coming out of the reactor, meaning either too much CO2 is being added, flow rates are too high or a combination of both. The reactor may also be too small for the demand of the system or be of poor quality and design.

Another alternative to adding more CO2 would be to add kalkwasser instead which actually reacts with the CO2 in the tank promoting a higher and stable pH.

I don't think anything over 10 dkh is good for SPS, mainly because I've never seen a successful SPS tank with an alkalinity that high. Even if you go through RC TOTM I don't think you'll see anything with much higher than 9 dkh.