pH too hard to control

[rayray]

I can only keep my pH@8.2-8.3 for a few months before needing major tweaking again. This time I disconnected my calcium reactor and kalkstirrer for 1 week and upon returning from vacation found the "natural pH" of my 75g tank to be 7.9day, 7.6night. This setup previously led to amazing growth of SPS, clams and corallin (the rock is bright purple).

I am using ro/di H2O with Tropic Marin Pro salt and a pinch of Mg, I & Sr, 10% weekly water changes have a pH of 8.05. I cleaned and recalibrated all 3 pH probes, am having the Ca reactor and stirrer checked for malfunction at the LFS, but am frankly getting tired of chasing the pH.

I prefer simplicity as I have already had a close call with both units; despite each having its own pH controller and their powerstrips being controlled by the tank's reefkeeper controller with its own pH probe. Will it help to use an effulent chamber with the calcium reactor and get rid of the kalkreactor. Or get rid of the Ca reactor and use only kalk and let the pH stay where it is?

[cccapt]

Something doesn't sound right. With a ca reactor AND dosing kalk your pH should be higher. Have you calibrated your probes?
What's your alk?

[rayray]

I calibrated all 3 probes: 2x milwaukee controller probes, 1 american marine pinpoint. Last month dK=8, [Ca++]=500. The LFS says they have to buffer Tropic Marin Pro quite a bit to get its pH up to 8.3.

Could the solenoid to the CO2 tank or the check valves be bad?

Is there really proof that pH below 8 prevents calcification in SPS?

[cmor1701d]

What is your source water?
Take a sample of your source, let it sit overnight then test the pH. You may have acidic source water which is using up your buffer. But, with your alk at 8dKH you should have plenty of buffering in the tank water. I agree with Larry. Something doesn't sound right.

[cccapt]

If your ca is 500, a balanced alk reading is about 19.5 dKH. Your chemistry is out of whack.

The LFS says they have to buffer Tropic Marin Pro quite a bit to get its pH up to 8.3.

What do they buffer with? Adding buffer also increases alk. You don't need to raise your alk, you need to let your ca drop. With your alk at 8 dKH, a balanced ca level is around 410.

Is there really proof that pH below 8 prevents calcification in SPS?

Here's a pretty in depth chemistry article by Randy Holmes-Farley.
And a little quote from the article..."It is well known in the scientific literature, if not in the reefkeeping hobby, that calcification is slowed considerably as the pH is lowered below natural levels. This result is especially concerning and is a hot topic of research because of the decrease in the pH of the oceans as CO2 is added to the atmosphere. The predictions of reduced calcification in coral reefs in the future are substantial."
It also says..."As the pH of the external fluid is lowered, it becomes harder and harder for cells to excrete the excess protons that come about from calcification. That is, they take in bicarbonate, strip off a proton, precipitate the carbonate into their skeleton and then have to do something with that proton. Many of those protons can be used to make CO2 out of bicarbonate, and may thereby boost the rate of photosynthesis. Still, not all of the protons may be used this way, and some will be excreted."

[Ziggy953]

Hmmm that is out of whack to quote ccapt. I don't know if using an effulent chamber or cup would really make that much difference but I think I would start there. I'd be very interested in seeing how this all plays out though. I'm not using a reactor on my system, yet, so Ive had similar concerns with adding the equipment.

[rayray]

I recalibrated all 3 pH probes (pinpoint) with fresh packets & found the one in the main display was always 0.2 lower than the other 2 in the stand so im replacing it (only 6 months old). I made an aeration trough, 1' long tray that the effulent can sit in before getting drained into the sump to diffuse CO2, and replaced a door to the stand with a 20" fan to aerate, but the wife says it looks ugly. An effulent chamber is pretty expensive; I may buy 1 if my DIY trough works. Ca levels dropping to 400, dKH 9 (salifert), but all SPS still have growing tips. pH still swings a lot, 8.2 @ end of photoperoid, 7.9 night; next day 8.15 to 7.85, and so on down so that I need to constantly drip kalk to raise pH. That was the kalkstirrers job!!! Source water pH is 7.9 (that I buy from a reputable LFS), goes to 8.1 with tropic marin pro salt. Maybe I should stop treating the pH numbers? This is proving to be a lot of work.