Sodium bicarbonate vs sodium carbonate
 

Any opinions and experience about which is better? In the past have used sodium carbonate (from Seachem), but in the last year have gone to the much cheaper bulk bicarbonate. My SPS growth has not been as fast lately (but there may have been other reasons).

I have not tested my pH for a long time,... maybe I should. Does higher (and consistent pH) make a difference to SPS? The carbonate is supposed to be better to maintain a higher pH.

Some people find benefit to switch to carbonate during the winter when low pH can be a problem. Most tanks do just fine with bicarbonate. I haven't used carbonate for many, many years. If you test pH use a calibrated pH meter.

Does lower pH affect SPS growth?

If it's low enough (or high enough for that matter).

I am sure my pH varies from day to night time. What range do you consider good for SPS? Or conversely, what pH is bad for SPS?

I dose carbonate that I buy in powder form at J&L and mix myself. I use dosing pumps that come on once an hour and my ph stays at a steady 8.2. I stopped testing it years ago though cause I found that if you keep your alk in check your PH will stay stable, at least in my tank it does.

For coral growth I've found alk and calcium levels are more important than chasing ph. Aim for stability and your system will run right unless you maintain a stable number that is way off the charts or something like that.

I've heard claims like "SPS need alk of 12" or "PH has to be 8.4" over the years but I run a very successful sps system with my alk at 7.8 - 8.

I really don't think there are perfect numbers, only acceptable ranges for all reef tank numbers.

Ok, I've rambled enough...lol

It probably does. Most SPS tanks will start to suffer below 7.8 and above 8.4. Ideally, you want to be around 8.2-8.3, but as Chin says, don't chase the pH too much. Remember that pH is a result of several factors. It's like baking a cake...err...it's like a carburetor, you gotta get the mix right or it doesn't run properly. The "mix" primarily being CO2 and oxygen - though the source of CO2 (causing acidification, or lowering of pH) isn't always obvious.

Well, in that case I should maybe switch back to using carbonate. That is supposed to keep pH closer to 8.3. I still have a fair bit of bicarbonate left, though, so won't happen for a while yet. Meanwhile will do some pH testing at different times of the day, and see what mine is really at.

Sodium carbonate is also more concentrated because it isn't "hydrated" like bicarbonate. If you want to get real crazy you can dose carbonate at night and bicarbonate at day. :p

I did a couple of pH tests and results were pretty well as expected. In the afternoon, after lights have been on and bright for quite a while, the pH was 8.2. In the morning, before the lights have ramped up, the pH was 7.8. So it is within range, but not totally consistent. I guess the C02 buildup overnight is what drops it.

My test kit (API) is pretty old too, so results may not be totally accurate, although seemed to be what I expected.

Not sure what the results would be with the carbonate (vs the bicarb that I use now). I don't recall what my tests were (long time ago) when I was using sodium carbonate so have nothing to compare to.

Now the question is, should I switch to carbonate for my alk dosing?