Randy Holmes-Farley
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My Tank Thread
I’m trying to raise it, not maintain. The AFR I’m dosing seems to keep up with consumption already, but I feel 1250 is a little low and I’d ideally would like to be at 1350. So I’m just trying to bring my baseline up 100ppm by adding the 235grams of powder I calculated.
How are you measuring that 1250 ppm and what is the salinity?
I know that is what you are trying to do, and it's fine to do it as long as magnesium is not a lot higher than you think.
I'm simply expressing the opinion that the 1250 ppm value noted may be subject to massive potential error, and 1250 ppm is not a big issue anyway. Much of the ocean where corals grow is near 1250 ppm magnesium.
At 24 mL per day of AFR added to 150 gallons, you are adding:
1.8 ppm calcium
0.04 dKH of alk
0.01 ppm of magnesium
The actual ongoing depletion of magnesium will be no higher than 0.2 ppm per day. Likely less. So to drop from 1300 ppm to 1250 ppm would take 250 days, assuming no water changes that would also add magnesium if the salt mix is at least 1300 ppm.
So if you have been doing this dosing for 250 day without water changes, the 1250 ppm is quite plausible and adding some is fine.
If you have not been doing it that long or have been doing water changes, then I expect the low value is either test error or low salinity.
The latter can be fixed by raising salinity or doing the addition you mention, but the former is the concern. What if magnesium is really already 1400 ppm and this value of 1250 ppm is test error?