magnesium

[Delphinus]

2400 seems awfully high. I agree with Mark that this sounds possibly a bad test reading. I can't even get a reading that high on my Mg test kit unless I refill my titration syringe.

950 sounds believable. (Low, but believable.) Depending on salt mix, Magnesium readings vary quite a bit and some have low Magnesium. You should test your freshly made water change water so you know what Mg value you're working with. I have to add a fair bit of Mg to my water change water otherwise I pull the Mg down with every water change. You want to aim for around 1500-1600.

If that PO4 reading ppm? If so that's not too bad a reading. PO4 readings vary hugely from day to day and even time of day. If I take a PO4 reading half an hour after I feed the tank I can expect it to read anywhere from 8 to 20 ppb and if I take a reading in the morning 12 hours later I get a legit 0 reading (I use a Hanna handheld).