Boosting Mg, Double Check Requested :)

[VR28man]

So, in my 30 gallon SPS tank my Mg is 1260 mg/L. ATI's reference value is 1412*, for a difference of 152 mg/L.

I got a fluval Mg additive: it advertises that 5ml will raise 20G of salt water 5mg/L. So, I calculate for my 30G I will need to add about 228ml of Fluval Mg supplement to raise the Mg by 152 mg/L. Do you think this is correct, or did I mess up my calculations?

I assume that, if I do this, I should not add all 228ml at once, rather add it in maybe 20ml increments over 11 days?

(ETA: Randy's article says "I would not suggest raising magnesium by more than 100 ppm per day under normal conditions, in case the magnesium supplement contains any toxic impurities. If you need to raise it by several hundred ppm, spreading the addition over several days will allow you to more accurately reach the target concentration, and might possibly allow the aquarium to handle any impurities that the supplement contains (such as ammonia or trace metals).". So it seems I can do it in as few as two increments? I still would rather do it over the course of 4 to 5 days)

(*I am using ATI essentials so I'm using their recommended reference value; discussion of whether I should do that or not monkey with my mg because it's near ocean value is welcome)

 

[chipmunkofdoom2]

Your math appears to be right. Your tank is about 1.5 x bigger than the example tank (30 / 20 = 1.5x). So, you will need about 1.5x more supplement to raise your tank by the same amount as the example tank. A 152 ppm increase in a 20g tank will take about 152 ml. So in your tank, which is 1.5x bigger, you'll need about 228 ml (152 * 1.5 = 228 ml).

As to whether you should raise your Mg to 1,412 ppm, I guess it depends where you're running your calcium and alkalinity. Calcium and alkalinity near seawater levels are likely fine with Mg levels close to natural levels as well. If you're running higher alk and Ca, it might be beneficial to have higher Mg to discourage precipitation.

Personally, I would probably not try to raise it too much unless your salt mix has Mg around your target value. If it doesn't, every water change you do will actually lower your Mg, and will require more dosing.