low pH, very low alk/calc demand, no SPS growth

[pluikens]

I've been keeping SPS for a few months now and I'm not seeing any noticeable growth from them. I know acropora are slow growers but I've had some montipora in the tank since November and they haven't even encrusted the frag plug. I'm set up to dose BRS two part for Mag/Alk/Calc but my demand is extremely low. I have polyp extension during the day on my SPS but now visible growth. I believe this is related to low pH so if this could be confirmed or another potential cause is identified, it would be greatly appreciated.

40 gallon tank, 20 gallon sump
5-6 gallon refugium growing chaeto on opposite light schedule (unless pH is below 7.5, then ON)
Two AI Prime HDs running AB+ from noon to 7 with two-hour ramps on either side
Temp: 78 degrees
pH: daily swing between 7.35 and 7.64, an average of 7.48
Mag: 1480 (Red Sea)
Alk: 9 dKH (Hanna)
Calc: 475 ppm (Red Sea)
PO4: 0.02 ppm (Hanna ULR)
NO3: 2 ppm (Red Sea)

Calc Demand:
I'm trying to lower my calc to around 450 ppm so I'm currently not dosing it. It's dropping slowly and I have my doser ready to turn on once levels drop below 450.
Alk Demand:
BRS Soda Ash is dosed 2ml every evening keeping alk right around 9 dKH. Using the BRS calculator, this comes out to a daily consumption of 0.06 dKH.

So, is my low consumption of alk/calc and slow/no growth due to low pH or something else? What would you try to get frags growing? Keep in mind I'm not expecting explosive growth but it would be nice to see growth after a few months. Thanks in advance!

 

[saltyfilmfolks]

What’s your par roughly near the acros?
How long is the photo period?

I think your ph probe needs calibration.

 

[pluikens]

I just recalibrated my pH probe on Friday but it is spiking due to interference from pumps. I'll bring some water to my LFS to confirm my readings tonight. As for the PAR, the units are about 8" over the water and my acros are no more than 6" below the surface so PAR should be between 250 and 300 based on BRS tests of multiple AI Prime HDs.

 

[vegamedic]

Have you considered switching your alk supplement to sodium hydroxide instead of soda ash? I'd be suspicious that the low pH is depressing coral growth, using NaOH would bump your pH up.

 

[pluikens]

Have you considered switching your alk supplement to sodium hydroxide instead of soda ash? I'd be suspicious that the low pH is depressing coral growth, using NaOH would bump your pH up.

Would that mean switching to kalkwasser rather than the soda ash and calcium carbonate? If my low pH is suspect, I'm considering adding a co2 scrubber before changing additives but I'm not against it once the 2 part I have runs out. I live in Minnesota so the house has been pretty closed up since probably October so it may just be a seasonal thing when I need to run the scrubber.

 

[pluikens]

Have you considered switching your alk supplement to sodium hydroxide instead of soda ash? I'd be suspicious that the low pH is depressing coral growth, using NaOH would bump your pH up.

Or are you suggesting I stop my small dosing of Soda Ash and dose something like aquavitro balance to increase just alk and pH?

 

[vegamedic]

Or are you suggesting I stop my small dosing of Soda Ash and dose something like aquavitro balance to increase just alk and pH?

I'm talking about using Randy's new recipe for the alkalinity part of your 2 part dosing. Instead of dissolving soda ash in water and dosing it, you dissolve sodium hydroxide (lye) in water and dose that. It has a very high pH itself (~14 iirc) and the way it raises alk also raises tank pH slightly. Mine 60g went from ~7.8-8.0 to 8.1-8.3 over the course of the day when I switched.

 

[jda]

I suggest that you unplug the PH probe and never look at PH again. Keep the alk stable and do not sweat the PH... ever. People do damage chasing PH.

Soda ash for an alk supplement is fine.

Your tank looks pretty new. It can take a while for SPS to grow in new tanks, and even longer in new tanks started with dead rock. If not yet a year, then just be patient and things should pick up when your tank gets more mature.

 

[Velcro]

I suggest that you unplug the PH probe and never look at PH again. Keep the alk stable and do not sweat the PH... ever. People do damage chasing PH.

Soda ash for an alk supplement is fine.

Your tank looks pretty new. It can take a while for SPS to grow in new tanks, and even longer in new tanks started with dead rock. If not yet a year, then just be patient and things should pick up when your tank gets more mature.

To an extent, but if his pH is really that low it could be an issue. That's down in calcium reactor territory if running the steady stream method.

 

[vegamedic]

I suggest that you unplug the PH probe and never look at PH again. Keep the alk stable and do not sweat the PH... ever. People do damage chasing PH.

Normally I would agree but the pH range we're talking about (7.35-7.65) will have negative effects on coral calcification as shown in many easy to find papers. It's very likely that the zero to low SPS growth OP is seeing is directly related to the carbonate buffer system in their tank being deranged, which is reflected by the low pH. It may also impact fish health but that's definitely not may area of expertise.

OP: I would try a couple quick rule-outs that are good husbandry practices anyway.
1) Your profile says you're in MN and I imagine you've got the windows closed and the heat on. Find a nicer day this week and crack the closest window to the tank to get some fresh air in the area and see if that has an impact on your readings. How big is your house and how many people live in it?

2) Are you using RO/DI water, and if so, how new are the cartridges? What is the pH of your freshly mixed salt water, assuming you do regular water changes?

3) Besides 2-part, are you adding anything else to either the tank itself or your topoff/WC water?

 

[jda]

Ph of 7.35 is almost impossible in a tank with any aragonite unless you are directly injecting CO2 into the water. I would guess that the probe is messed up.

Even in a closed up house in Missouri (all year) with five of us, 3 dogs and a CaRx, the lowest that I could get was a legit 7.85, which is fine.