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Alkalinity matters

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Tank alkalinity has been somewhat low but I couldn't figure out why. My calcium reactor was full of media, the CO2 tank was full of gas, everything looked right. That's when I realized I was missing the point, that the pH measurement inside the reactor was not where it belonged. Normally it's between 6.1 to 6.5 depending on my mood, so to speak. The pH controller showed that it was 7.5 and my brain didn't click, that it wasn't 6.5... dumb mental error. In the meantime, I labeled that spot with my target numbers to avoid ever doing that again... though I'm reasonably sure that it won't happen again after this. lol

I had to clean out an inline check valve on the calcium reactor that was sealed shut with salt creep, which prevented CO2 from entering the reactor. That's been corrected, and the controller was forced to a lower set point to help get my tank's alkalinity back up to normal levels. It's been stuck at 7.5 dKH for some time, as of last night it's reading 10.5 dKH. I prefer somewhere closer to 10. When 6.5 wasn't cutting it, I dropped it to 6.1.  That didn't do it either, so after some measurements I lowered it to 5.7 on the controller (which is a significant drop) but I was dealing with a faulty probe and I've got nearly 15 years experience with this reactor and just needed to solve the problem until new parts arrive.

I've burned through a brand new Elos alkalinity test kit doing some serious testing over a 24 hour period. I wanted to know a few things:
What is the pH in the reactor?

What does the pH controller state is in the reactor?

What is the alkalinity of the tank?

What is the alkalinity of the effluent?

What is the alkalinity of alkalinity solution (2 cups Soda Ash to one gallon RODI)?

And my answers after a couple of days of scrutiny:

pH in the reactor was 6.12
pH reported by the controller was 5.8

This means I need to replace the pH probe since it's old, and that's going to require me to buy a new pH probe holder as well.

Alkalinity of the tank was 7.5 dKH for nearly a week, down from 9.5.
I dosed soda ash every other day to help buffer the situation while I was trying to resolve whatever was going on.

Alkalinity of the effluent measured 70 dKH.

Typical effluent should measure between 19 and 35 dKH. 70 dKH was because I ran the pH down hard trying to overcome the 7.5 it seemed to be stuck at. It was visibly too low because the water in my reactor was cloudy grey, instead of clear. After I was done with testing, I raised the pH slightly and the water within has turned clear once more. 70 dKH is crazy high, and I've slowed the output from a normal trickle to a semi-decent drip to avoid raising alkalinity too much at the moment. Now that the tank is sitting at 10.5 dKH I don't want it to go higher.

Alkalinity of the mixed Soda Ash measured over 180 dKH.

That's why I nearly wiped out my test kit in one day. I filled the beaker with so many drops that it was full before I got the color change. I've never tested dKH of mixed solution so I was curious what it measures. If you've measured it or would like to measure yours, I'd love to hear what value you get.

My reef is doing just fine despite the minor alkalinity drama, and all my crazy numbers. I was on a fact-checking mission this week to gather some intel and answer some questions I'd pondered about for some time.


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