Help, something is causing “suppression” of pH?

E13MentX · Apr 14, 2024

I have been chasing elevated pH for over a year now and I had great success. I was very happy with the results. However for whatever reason I am unable to achieve similar pH levels (8.3-8.6) I previously had despite keeping everything the same in my 150 gallon tank. I am using the following methods to increase pH (same as before) recirculating co2 scrubber, Kalkwasser through a stirrer 11L at night, recently added algae scrubber, keep house co2 400-600, dose sodium hydroxide to make up the difference between alk and calcium in Kalkwasser. As you can see from the charts I used to maintain fairly high pH with all my methods. But recently past few weeks, using the same methods I have been unable to raise it back to previous levels. Is there another cause? The only change that I know that happened was that I siphoned the sand since I spilled rowaphos when the media reactor lid came off into my tank which I don’t usually do. But I recalibrated both pH probes (I do this monthly but I double checked again), change co2 scrubber media, clean the skimmer just in case it wasn’t pulling as much air, added new fresh Kalkwasser to the stirrer but I am barely getting above 7.9 at times. Is there an underlying cause? Or are there other means I can increase the pH? I thought maybe disturbing my shallow sand bed (0.5-1 inch) may have increase organics which lowered the pH. But I have done large water changes and also refreshed the carbon as well as added ozone to the tank but I still cannot increase my tank pH. Any help would be appreciated. Thanks!

Randy Holmes-Farley · Apr 14, 2024

pH is determined mathematically by CO2 in the water and the alkalinity.

If pH is actually different (as opposed to test error, maybe get new calibration buffers) at the same alkalinity, then it must be from changes in CO2 in the water.

The CO2 in the air, of course, can change the CO2 in the water. You give a range from 400 to 600 ppm, which if fully equilibrated will result in about a 0.18 pH unit change in the pH.

You do not mention the alkalinity, but the difference between 7 and 11 dKH equates to a difference of about a 0.2 pH unit change. Has the alk changed?

Also, adding hydroxide to maintain alkalinity raises pH, and the more you add the higher the pH effect, even to maintain the same alkalinity. Do you know the potency of the kalkwasser you are using and the volume dosed, and has that possibly changed? There's a bit of a positive feedback loop here. pH dropping lowers demand which lowers hydroxide added to maintain alk which lowers pH again, repeat repeat.

If the scrubber media working similarly? Not depleted? Not channeled?

Are the photosynthetic organisms being limited by a trace element such as iron, or a nutrient such as ammonia/nitrate or phosphate?

Uncle99 · Apr 14, 2024

Probes can go out of calibration.
Are you sure the results are accurate?

I chased PH once decades ago.

Now I don’t care what it is.

E13MentX · Apr 14, 2024

Randy Holmes-Farley said:
pH is determined mathematically by CO2 in the water and the alkalinity.

If pH is actually different (as opposed to test error, maybe get new calibration buffers) at the same alkalinity, then it must be from changes in CO2 in the water.

The CO2 in the air, of course, can change the CO2 in the water. You give a range from 400 to 600 ppm, which if fully equilibrated will result in about a 0.18 pH unit change in the pH.

You do not mention the alkalinity, but the difference between 7 and 11 dKH equates to a difference of about a 0.2 pH unit change. Has the alk changed?

Also, adding hydroxide to maintain alkalinity raises pH, and the more you add the higher the pH effect, even to maintain the same alkalinity. Do you know the potency of the kalkwasser you are using and the volume dosed, and has that possibly changed? There's a bit of a positive feedback loop here. pH dropping lowers demand which lowers hydroxide added to maintain alk which lowers pH again, repeat repeat.

If the scrubber media working similarly? Not depleted? Not channeled?

Are the photosynthetic organisms being limited by a trace element such as iron, or a nutrient such as ammonia/nitrate or phosphate?

Thanks for the fast reply @Randy Holmes-Farley. My alkalinity goes from 8ish to 9ish throughout the day. When I first started chasing pH my alk did spike up initially but slowly as demand increased it leveled out in a few months. The alkalinity has not really changed for the most part in the past 6ish months. My Kalkwasser should be fully saturated I add 2 cups every 2-3 weeks in the stirrer and 1 cup over the max saturation according avast marine. I have tried to measure the pH on the kalk stirrer but I did not have consistent results with it. I’m assuming it is saturated but I have not changed my refill method since I introduced the stirrer. I tweaked the sodium hydroxide (your recommended concentration) according to my calcium. Since I mostly used Kalkwasser and reef crystals I tend to get high calcium over time auto water change of 3.5L a day. But it is minimal dosing compared to my Kalkwasser. I know the scrubber media is working because I definitely get a drop when I tried to pull outside air instead of using the co2 scrubber. I recently did a ICP test and I actually slight excess iron and extremely high iodine since I was over dosing trace combo. But I have since then done massive water changes to mostly reduce the excess. I dose nitrate I try to keep it around 5-10. Phosphate I always had issue with since I over feed pellets and I use rowaphos and now algae turf scrubber. I try to keep it under .1 and not 0 ppm. I hope that was enough info to help get a better picture of the situation.

E13MentX · Apr 14, 2024

Uncle99 said:
Probes can go out of calibration.
Are you sure the results are accurate?

I chased PH once decades ago.

Now I don’t care what it is.

I have 2 probes since I chasing pH I wanted to make sure I was chasing the correct pH. They are both within 0.05 of each other and I alternate calibrating them every month. Since I found this issues. I have tested against different standards and recalibrated multiple times to be sure. I understand that pH may not be important for some but I had success chasing it and would like to continue if I could.

Randy Holmes-Farley · Apr 14, 2024

E13MentX said:
Thanks for the fast reply @Randy Holmes-Farley. My alkalinity goes from 8ish to 9ish throughout the day. When I first started chasing pH my alk did spike up initially but slowly as demand increased it leveled out in a few months. The alkalinity has not really changed for the most part in the past 6ish months. My Kalkwasser should be fully saturated I add 2 cups every 2-3 weeks in the stirrer and 1 cup over the max saturation according avast marine. I have tried to measure the pH on the kalk stirrer but I did not have consistent results with it. I’m assuming it is saturated but I have not changed my refill method since I introduced the stirrer. I tweaked the sodium hydroxide (your recommended concentration) according to my calcium. Since I mostly used Kalkwasser and reef crystals I tend to get high calcium over time auto water change of 3.5L a day. But it is minimal dosing compared to my Kalkwasser. I know the scrubber media is working because I definitely get a drop when I tried to pull outside air instead of using the co2 scrubber. I recently did a ICP test and I actually slight excess iron and extremely high iodine since I was over dosing trace combo. But I have since then done massive water changes to mostly reduce the excess. I dose nitrate I try to keep it around 5-10. Phosphate I always had issue with since I over feed pellets and I use rowaphos and now algae turf scrubber. I try to keep it under .1 and not 0 ppm. I hope that was enough info to help get a better picture of the situation.

FWIW, I’m not a fan of kalk stirrers due to the fact that they often do not produce the saturated kalkwasser users assume.