Ridiculous pH problem...out of ideas

[boobookitty]

I have a 400G, about 3 years old. I’ve had reef tanks for 20+ years, including a 240G for a decade that did very well. Took it down 6 years ago, started the 400G 3 years after.

The problem is my pH. It’s swings between 7.85 during the day down to 7.65 at night, sometimes down to below 7.6. I know not to chase numbers, but that seems reeeeaally low, and I’ve suffered for a year and a half from periodic coral colony rtn’s (good growth until then), sometimes part of a colony, sometimes the whole thing, and I think it’s related.

Basic equipment

- 400G tank, 100G sump/fuge
- 8 Radion 30 pros, 20KK profile
- flow provided by Vectra L1 return on a sea swirl (old school!), an MP60, 3 Wavs, and a Panta Rhei.
- Dastaco CA reactor
- SRO Ext-6000 skimmer
- vodka dosing for control of nitrate
- GFO for control of phosphate


Parameters:
- alk 8.0
- CA 450
- Mg 1450
- Nitrate 1ppm
- phosphate 0.15 (been slowly lowering it from 1.5 6 months ago)

I had a nutrient problem that built up over a couple years; tried controlling it with zeovit, which worked well on my old tank but not on this one, and switched to vodka dosing and GFO, which has worked well to substantially lower them. I had thought the stn problem might have been that, but even with lower nutrient I have this issue.

Over the last few weeks I’ve tried to get the pH issue in hand:

- I’ve had tubing providing outside air as the skimmer air intake for a year or so; added CO2 scrubbing to it; this helped a little, but still left me with 7.65 at night
- punched a hole through my wall to the outside a couple weeks ago and have fresh air flowing across the top of the tank; this raised pH minimally, around 0.05
- flowed the fresh outside air across the sump; this didn’t raise pH at all
- Dastaco’s can deliver CO2 through the effluent return, so I had this drop into a tube that flows into the sump to try to avoid CO2 getting into the sump area; a few days ago I added a funnel to the tubing and raised the effluent return an inch, and added a fan blowing across the funnel to keep CO2 from settling into the sump; this actually helped some, around +0.05 pH


Even with all of the above, the best I can get pH during the day is 7.89-7.9, and at night it still can drop below 7.7. Very frustrating. Looking for input regarding any other ideas. I’d prefer not to go to a chemical solution like kalk, but I will if that becomes the only option.

 

[Uncle99]

I have the same PH as you do, those numbers are not uncommon.
Carbon dosing lowers PH, other than that, I tried the fan thing, the outside air to skimmer thing, same numbers.
It is what it is, nothing I have ever found to date changed it (much)
Did get various readings from three different tests, one was 8.1.
Never pay any more attention to it.
Chemical solutions not recommended as the effect is temporary, maybe a day, and the up and down effects stability which is vital.

 

[ReefsandGeeks]

I've had the same issue and raised my alk a little which helped some, but didn't want to raise it any more. I've since build a CO2 scrubber for my skimmer air inlet which seems to help also. I never noticed a change in pH from opening a window, but the scrubber seems to work. Of course you have to keep buying media for it. I use medical kind for anesthesia machines or for re-breathers. it seems to work well.

Once I did this, my hard coral did seem to grow faster and be healthier. I went a long time without chasing the numbers, but this sis seem to help.

 

[thegrun]

Certainly adding a CO2 scrubber to your skimmer air intake will raise your pH and increase your stony coral growth, but it will not be inexpensive to keep buying the media for a large system like yours.

 

[ca1ore]

My tank runs 7.9-8.0 during the day; 7.6-7.7 at night. A little worse in the Summer. Using kalkwasser on your ATO can help.

 

[boobookitty]

Definitely appreciate all of the input. It was the Dastaco. Fresh air across the top of the tank helped a little bit, but now that I've replumbed the Dastaco effluent drip to drop into a funnel and blow air across it to blow out CO2 (the dastacos vent CO2 through the effluent tube), pH swung between 7.75 and 7.95 yesterday, and 7.8 and 8.0 today. This has plagued me for a while...wish I'd thought of that earlier. I had the effluent dripping into a tube outside the tank that then drained into the sump, but since CO2 is heavier than air it must have been dropping into the tube anyway.