I'm looking for a way to lower my ph as it is 8.6 which will not affect phosphates,,as I've discovered using ph down blows my phosphates threw the roof what can I use???????
I've been through most of RH-F's material on the subject and I don't recall there being any linkage between Mg and pH except alkalinity.
Also, if you find a need to dose Mg into a FOWLR tank, something may be wrong. There should be nothing using Mg but coraline algae, which is minute.
A decent water change schedule with a normal salt like Instant Ocean should be all it takes to keep parameters in line, maybe with exception to a little alkalinity dosing in some tanks.
So do water changes - 10-20% per week is recommended in most cases - and test+dose alkalinity as needed. pH should not be an issue then.