Interesting Magnesium Observation

[Myka]

As many of you know, I have about 30 Bangaii babies in a container in my 33g reef tank. They are causing a HUGE bioload, and have caused a massive hair algae bloom. My water column tests just a trace of Nitrate and just a trace of Phosphates, but it's obvious there's more in there. I added a PhosBan Reactor and put 2" of RowaPhos in the chamber, and noticed no difference after a week. So I figured what the heck, I'll try the ole raise the Magnesium trick. Up until this time I've kept my Magnesium in the 1350-1400 ppm range. So I've been doing waterchanges with 1550 ppm Magnesium, raised by Epsom salts. I honestly don't know what my tank is at right now because I haven't tested it, but I've done two 30% waterchanges with raised Magnesium. It really shouldn't be much higher than about 1450-1475 ppm. The hair algae has become significantly stunted.

So that's all fine and dandy, but here's what I've noticed. I always have a 5g bucket of saltwater mixing for waterchanges, but mostly because I need saltwater every couple of days to make new batches of baby brine shrimp. Now, usually I add the Epsom salts to raise the Magnesium just a couple hours before I do the waterchange, and use "normal" SW for my BBS. Well, three times I have used the SW with elevated Magnesium. In all three batches of BBS (using the same container of eggs) I have had VERY poor hatch rates. I mean I use 1/4 tsp in a 2L pop bottle, and normally when I syringe the BBS out there are so many in the syringe that it appears pink-orange and you can't even see through it. When I use the SW with elevated Magnesium you have to really look to notice there are any BBS in there at all.

So...is it the elevated Magnesium that's causing this? Or a sensitivity to the sulphates in Epsom salts?

AND...if BBS are sensitive to this (for whatever reason) what is it doing to my reef?

Either way, I have some SeaChem Magnesium on the way!