Magnesium
Dillute the sample you are testing for magnesium with RODI water to 50% or 75% strenght and retest. Multiply by your dilution to get the result....see if that matches with the first round of tests above.
FWIW, high Mg is rarely a problem. Likewise for high Ca. I've accidentally dosed my Ca to around 700 ppm, and if anything there was a color and growth spurt...no stress. Mg should be similar.
Phosphates
The only thing liquid PO4 tests are good for is diagnosing zero. If the sample has no color at the end of the test - not blue, not baby blue, not slightly blue, not barely blue or any of the other levels they laughably expect you to discern on those tests - your PO4 can be considered low enough. You always have to go by what the tank is telling you as well though...test kit can't tell everything, even when it's the best one.
Lighting
Download a lux meter onto your smartphone for free. If you want a handheld, they only cost around $15-$20.
-Matt
ok so when I diluted the mag test I come to 1680. (that was a great idea that I would not have thought of).
As for taking the lux reading how do I do it? do I point it at the top of the water? or right below the lights or even at the lights?
I did download it just don't know where to take the reading from