Unexplained Downtrend in pH

dangles · Jun 12, 2023

I have a 50g AIO that was cycled in January, and currently stocked with some fish and inverts. About 6 weeks ago I converted one of the back chambers into a small refugium lit by the AI Blade Refugium to help control nutrients (I feed heavily). Before the fuge, I was running between 7.8 and 7.9 pH. I was initially only running the light for about 6 hours a day but the chaeto was starting to die off so I ramped it up to 24/7 and started dosing ChaetoGrow and it bounced back really well. My pH then began to read between 8.05 - 8.15 reliably for a few weeks. I also manually dose BRS 2-part using soda ash to keep my dKH between 8.5 and 9.

However over the last couple of weeks my pH has been trending downward again and is now barely able to make it to 8.05 after my soda ash doses. Usually it's closer to 7.95-8.0. I considered CO2 but it's summer here and I've been keeping my windows open specifically to keep fresh air in circulating. It's just me and my dog, and I'm gone for 24 hours at a time. There haven't been any changes in CO2 sources over the last couple of months so I'm tentatively ruling out CO2 as the culprit for this recent downtrend. There also haven't been any meaningful shifts in trend for my dKH that would indicate consumption changes.

There have only been a couple of changes since I've noticed the downward trend... I added pods and started dosing phyto. And my water temps have gotten dialed in a little better (77-79.5 before, 77.0-77.5 now). Could phyto or slightly lower temps be contributing somehow? Is it possible I've had a few inverts die off and release some ammonia? Or if the film algae on the rocks is starting to die off (because the chaeto is outcompeting), would that release ammonia?

What other explanations could there be?

I realize it's not a huge swing, and that it's still within "normal" levels, and that it's not that important since it's currently just a FOWLR. But I will be adding corals at some point, and I would like to have everything dialed in and stabilized with my pH above 8.0 (slightly higher preferably) before then. Also, It's a good learning experience to think through these things and problem-solve. I want to understand WHY these things happen, not just how to chase numbers

Thanks!

Randy Holmes-Farley · Jun 12, 2023

pH measurement accuracy drift and reduced photosynthesis are possibilities.

The latter can come from something restricting organisms, such as N, P, or a trace element.

Ironic_Water · Jun 12, 2023

The first thing I would do is check the calibration on your probe. Get some pH probe cleaner and clean it before checking calibration (I use Hanna's cleaner both for my tank probe and at work).

Do a calibration, check what your probe reads when you put it in the calibration standards - just remember to get the standards to the same temperature as your tank water, otherwise it can affect accuracy. (I just put the pouch of liquid pH standard floating in my tank to warm it up)

Then, if your probe is reading right, you can go from there knowing you have good data.

dangles · Jun 12, 2023

Randy Holmes-Farley said:
pH measurement accuracy drift and reduced photosynthesis are possibilities.

The latter can come from something restricting organisms, such as N, P, or a trace element.

Thanks, Randy.

My nitrate has been holding steady around 5 and my phosphate has been around 0.03 for the last few weeks.

I checked/calibrated my pH sensors just a couple of weeks ago using tank-temp calibration fluids so as best I can tell it’s not a calibration issue (although I’ll check again to be sure).

dangles · Jun 12, 2023

Ironic_Water said:
The first thing I would do is check the calibration on your probe. Get some pH probe cleaner and clean it before checking calibration (I use Hanna's cleaner both for my tank probe and at work).

Do a calibration, check what your probe reads when you put it in the calibration standards - just remember to get the standards to the same temperature as your tank water, otherwise it can affect accuracy. (I just put the pouch of liquid pH standard floating in my tank to warm it up)

Then, if your probe is reading right, you can go from there knowing you have good data.

I didn’t know probe cleaner was a thing! I’ll check it out. Thanks!

dangles · Jun 12, 2023

Two thoughts I had while doing my maintenence today...

I forgot that I replaced my carbon with the Maxspect Nano-tech Bio Blocks (https://www.bulkreefsupply.com/nano...=15416&indexName=brs_prod_m2_default_products) about 2 weeks ago. I'm curious if that might have something to do with it.

Also, when I removed my refugium caddy to rotate it (it fits in one of the back chambers of my AIO), the chaeto was much denser than last time I removed it. Randy you had mentioned less photosynthesis and I wonder if because the chaeto is now getting denser, maybe the light isn't penetrating through the chaeto ball like it used to.

Randy Holmes-Farley · Jun 13, 2023

dangles said:
Also, when I removed my refugium caddy to rotate it (it fits in one of the back chambers of my AIO), the chaeto was much denser than last time I removed it. Randy you had mentioned less photosynthesis and I wonder if because the chaeto is now getting denser, maybe the light isn't penetrating through the chaeto ball like it used to.

That's possible. I doubt adding bioblocks lowerd pH.

dangles · Jun 15, 2023

pH has continued to decline, down to about 7.9 this morning.

My leading theory at the moment...

I was cleaning my tank this morning and again removed my refugeum for cleaning. This time I noticed the wall of the chamber that faces out (on the actual tank, not the refugeum caddy) was COVERED in thick algae. I hadn't looked at that last time, instead focusing on the caddy itself. It was blocking a large percentage of the fuge light from penetrating to the chaeto. I'm guessing the performance of my fuge has taken a huge hit over the last couple of weeks! That was in part confirmed when I did my weekly nutrient testing this morning and found that my PO4 had jumped from 0.03 all the way to 0.17 without any additional feeding or other changes

I cleaned out the chamber my refugeum caddy sits in, and did a large water change. I'll re-check my nutrients a few days earlier than normal to see if that did the trick. With any luck, I'll get an early clue that that's the issue if my pH starts to rise again!