Large alkalinity swings (2dKH over two weeks)

Randy Holmes-Farley · Jun 30, 2025

Obriy said:
This is the reasons ChatGPT provided why lower alkalinity is easier to keep stable. Could you, please, share your opinion o that?

Why 8 dKH is Easier to Keep Stable:

Lower Risk of Precipitation
At 10 dKH, especially if calcium and pH are also high, there's a greater chance of calcium carbonate precipitation— which can:

Drop alkalinity suddenly

Clog pumps/heaters with white buildup

Waste your dosing efforts

Slower Consumption Rate
Corals and coralline algae consume less alkalinitywhen it's at 8 dKH than at 10+, so:

Dosing needs are lower

Fluctuations are more gradual

Mistakes (like a missed dose) are less likely to cause sharp drops

More Room for Dosing Error
Dosing errors at higher dKH (especially with strong 2-part solutions) can spike levels quickly. A small overdose raises dKH faster when you're starting at 10 than when you're at 8.

Better Compatibility with Calcium & Magnesium
Keeping 8 dKH makes it easier to balance:

Calcium at ~420 ppm

Magnesium at ~1300 ppm
Without forcing unnatural ratios that increase precipitation.

Sure.

1 and 2 cause what I said: it takes more to keep higher alk because demand is higher.

3 is lame, and part is simply wrong. One could also say that at lower starting alk an underdose leads to too low of alk faster. The statement that dKH rises faster at higher starting dose is not correct.

4 is not accurate, nor is the idea that “unnatural” ratios increasing precipitation.

p1u5h13r4m24 · Jun 30, 2025

I’d like to add that I believe lower alk gives more room for nutrient error. If nutrients bottom out the higher alk would be more of a problem

spicymikey · Jun 30, 2025

Obriy said:
4/22/25
9.5
4/26/25
8.8
4/30/25
9.1
5/9/25
8.3
5/10/25
8.3
5/11/25
8.5
5/14/25
8.7
5/17/25
9
5/21/25
9.8
5/25/25
9.8
5/29/25
10.2
6/2/25
10.1
6/7/25
9.8
6/9/25
9.7
6/10/25
9.9
6/11/25
9.7
6/12/25
10.1
6/13/25
10.2
6/14/25
10.4
6/16/25
10.5
6/17/25
10.6
6/19/25
10.5
6/21/25
10.5
6/24/25
9.1
6/25/25
10
6/26/25
10.3
6/27/25
10.4

This is a non problem my friend. Things are going to fluctuate. That's one of the reasons it's recommended that you keep your total alkalinity in that 8-9 dkh range to be able to handle normal swings without going out of acceptable bounds. As someone else said you need to factor in time of day and any other things you may do between those readings with 1+ dka change. As long as you are steadily dosing the same amount of your preferred form of carbonate then no worries .

Ziggy17 · Jun 30, 2025

I recently had my alk ratchet up from 8.5 to 9.8 in a day. I changed out the tubing from the reservoirs and reprimed and then recalibrated, but left the program as it was. Turns out the new changed tubing was adding more alk than the old tubing, likely clogs. I just shut down the alk pump, kept the AFR going, and let it drop naturally of about .3 dkh every day. Corals including LPs showed no sign of being stressed.

All part of the fun ol chap.