Dosing Mag cause a PH swing

[homer1475]

I started dosing Mag yesterday as my levels were really low, 1180 end of the week to 1240 on a fresh water change, even though my fresh seawater measured 1320(reef crystals)

So after putting in the recommended dose, i let it sit for 24 hours before testing. Levels went up like expected but only by 40(1280 it was 1240 yesterday when I did a pretest). but my rock solid PH dropped a bunch, from a solid 8.4 since I setup the tank 3 months ago, down to an even 8.

So my question is, what would cause a PH drop like this, and could it be the mag I'm adding? Nothing else has changed in my tank other then the addition of a large Hawaiian feather duster. Should I be worried? I know 8 isn't terrible, but I would like it a bit higher.

[ReefkeeperJames]

With levels that low of Mg you can't even achieve a pH of 8.4 so I doubt you were even at 8.4 to begin with. Time of day can effect pH levels. Focus more on kH, Ca, and Mg.

[Stackemdeep]

While I do not know the exact product for Mg that you are using, Randy's Recipe which I use and most blends of Magnesium Chloride and Epsom Salts will have no appreciable effect upon pH.