Mag, Alk, Calcium


Premium Member
I need some help figuring out my reef chemistry. I have been testing my levels for the past 16 days and have noticed that after I dose magnesium the level continues to rise for several days after dosing before it levels out. It has done this three times now. Initially my mag level was 1050. I dosed to bring it to 1300 (I'm using liquid magnesium from Bulk Reef Supply and using their dosing calculator on their website). However, the level was not 1300 on my next check 24 hours later, it was 1260. Given this was the first time I was dosing my tank, I wanted to get a feel for how the levels were rising and falling, so I didn't dose again. I measured 24 hours later and the level was 1340. I figured this was good so I didn't dose anything additional. I measured again 24 hours later and the level was 1410. Again I didn't dose, and remeasured 24 hours later. The level had finally topped out as the reading was again 1410. It the level stayed stable for several days then started to fall. I let it fall through the 1300's to see how fast the level dropped so I could get an idea of what my daily maintenance dosage would be. When I hit 1250, I dosed again (based on the calculator on BRS website). The same thing happened again. This time, 24 hours after dosing, the level was 1320. I figured "good" this was in line with how much the level should have risen and I didn't dose again. Measurement of the level 24 hours later showed that it had risen again to 1390, and measurement 24 hours later was 1420. The level topped out at 1420, stayed there for several days, and then started to fall again. So my questions are, why is the level doing this? Ans, since the levels don't rise and stabilize after 24 hours, I'm thinking that I'm not going to be able to just calculate a daily dosing amount as the levels don't seem to rise predictably and take several days to start falling again.

I'm seeing a similar issue with my alk levels. At first the levels would rise as the should based on the calculator at Bulk Reef supply (I'm dosing their liquid soda ash). But after my last water change, I have only been able to get my dKH up to 9.9 (I'm shooting for 11). I've dosed the amount recommended by the dosing calculator for the past two days, but the dKH hasn't budged past 9.9.

Calcium is the only level that is acting predictably with dosing calculation and currently is 445 with a target of 450.

Water volume is 49 gallons. Salt mix is reef crystals. Salinity is 1.024 and stable. Temp is 78.8-79.3 and stable.