I did a quick search on this forum for "Magnesium" and couldn't find anything about how it affects algae growth. I know a big plus with ATS is less frequent water changes. Do most of you dose/test magnesium? The reason I ask is that there is 1 magnesium atom in every chlorophyll and I would imagine algae scrubbing will cause an higher depletion of magnesium compared to similar tanks without an algae scrubber.
I guess I haven't really noticed a huge problem with Mg depletion. I try to keep this element at about 1325ppm. I use Salifert to test Mg and I only check it about once every 3 months on most tanks. At that point, the most I usually have to increase it is by 100ppm, which is the recommended daily maximum for BRS Mg. I suppose when it drops down to the 1200ppm range, this might affect things, but it takes so long to get there. The thing that seems to drop much faster is Potassium. This is supposed to be at about 400, I tested my 3 tanks and found all 3 below 300, and one at 200. I got them all up to or above 400 over the course of a week, and if it weren't for forgetting to plug in the LED driver after cleaning one unit, I would have an idea of the uptake rate now. If you think about it, most fertilizers for plants have a N-P-K ratio. Algae is the same.
I have run a number of scrubber configurations for a couple fo years and i rarely need to dose magnesium, so little in fact that i dont even have any made up or connected, current system of 450L (120G US) has been running for 4 months and i have not dosed magnesium at all, i do very few water changes and do not use any salt with elevated levels. Potassium isnt something i measure that often but the last test indicated it was just over 400, time for another test perhaps...
