Dosing soda ash with a CO2 scrubber causing precipitation?

nickmealey · Apr 22, 2022

I'm currently dosing BRS 2-part Soda Ash and Calcium in a 150gal system. Over the past month I've been monitoring and adjusting dosage amounts with a goal of 8.5-9dkh and maintain a high a PH (~8.3). I've hooked up a CO2 scrubber to my skimmer and it works great. I have a solenoid valve to regulate the PH levels.

I can't seem to maintain an Alk of above 7.5dkh when the skimmer is circulating through the scrubber. My suspicion is that the PH level in the skimmer runs really high (> 8.5?) and it precipitates out. I tested this by bringing the scrubber offline and running the skimmer as usual and I was able to maintain desired Alk levels easily. However, this drops my PH significantly (~8.0).The tank has some coral in it with a low to medium load. Dosing as much as 200ml/day has no effect on Alk when the scrubber is running (stuck at 7.5dkh). With the scrubber offline, I can maintain 8.5dkh at about 70ml/day. It's possible that the increased PH means more Alk consumption, but this seems like a pretty decent jump. Also I tested this theory a bit by testing at the same PH levels with and without the scrubber and it seemed to have a major impact.

All that is to say, I'm considering switching from Soda Ash to Sodium Bicarb. Since this is basically baking soda, I'm wondering if there's a recipe to use baking soda along with the BRS calcium chloride? It sounds like since sodium bicarbonate doesn't affect the PH it has less precipitation issues.

A few things to highlight since I know it will be asked:
- I've recently calibrated my PH probe
- MG levels are within an acceptable range (~1400)
- Calcium levels seem balanced as far as I can tell (~380)
- Using Hannah checker for Alk levels

MnFish1 · Apr 22, 2022

1. Your Ca is a little 'low'.
2. BRS has a calculator for using baking soda to adjust alkalinity as well.
3. Have you tried measuring the pH in your skimmer when your CO2 scrubber is running?
4. If precipitation was happening due to the skimmer - it would SEEM to me that you would see it in the skimmer or near the skimmer.
5. Is it possible that your alkalinity and CA are being released near enough to each-other that when your pH does go up - that there is some precipitation happening due to that?
6. Do you does alkalinity and Ca at the same time/together? spreading them apart in time could help?
7. Do you see other evidence of precipitation in the tank, equipment, etc?
8. Where is your solenoid valve? If you just let your skimmer run 24/7 what would your pH be?
9. Are you measuring alkalinity/pH at the same time of day?

I would CONSIDER - running your skimmer 24/7, and dosing less alkalinity - and see what happens over a week or so - there should be no 'risk' - with an alkalinity of 7.5 vs. 8.5

nickmealey · Apr 22, 2022

MnFish1 said:
1. Your Ca is a little 'low'.
2. BRS has a calculator for using baking soda to adjust alkalinity as well.
3. Have you tried measuring the pH in your skimmer when your CO2 scrubber is running?
4. If precipitation was happening due to the skimmer - it would SEEM to me that you would see it in the skimmer or near the skimmer.
5. Is it possible that your alkalinity and CA are being released near enough to each-other that when your pH does go up - that there is some precipitation happening due to that?
6. Do you does alkalinity and Ca at the same time/together? spreading them apart in time could help?
7. Do you see other evidence of precipitation in the tank, equipment, etc?
8. Where is your solenoid valve? If you just let your skimmer run 24/7 what would your pH be?
9. Are you measuring alkalinity/pH at the same time of day?

I would CONSIDER - running your skimmer 24/7, and dosing less alkalinity - and see what happens over a week or so - there should be no 'risk' - with an alkalinity of 7.5 vs. 8.5

Thanks for the reply.

1. Yeah it is a bit low, but it's also what my salt comes in at naturally (Tropic Marin classic). Would too low Calcium cause precipitation?
2. I checked here and didn't see it
3. I've been meaning to check this but haven't yet. Soon hopefully

4. I'll have to pull the skimmer out and take a look. The cup of course is a dark dark brown so it's hard to tell with all other junk
5. The dosing tubes are downstream of the skimmer (return chamber), so I think it should have plenty of time to mix before reaching the skimmer.
6. I dose them in the same area of the sump, however they are spread out in intervals throughout the day about 30min apart. (I use the Neptune Dos)
7. Not that I can tell but I should open up some pumps and so forth.
8. The inlet of the skimmer. It would depend on the media and how fresh it is, but I imagine it would exceed 8.5 on a fresh load of media.
9. Yep

So just after seeing this I checked the dosing tubes and the wire from the return pump was obstructing the Alk drip and has a bunch of white buildup on it.

I'll have to do some organizing of some things and make sure the drip is unobstructed. I'll try and get back to just a "baseline" and follow up with what I find.