I like Salifert or Red Sea. I have several titration tests for
FW and
SW from each.
I also like the Hanna
PO4 checker. Can't beat it if you are planning a reef setup and want to know how much
PO4 is actually in the water. The
PO4 titration kit is just too hard to read accurately at the low levels you are trying to detect.
I also use a Milwaukee SMS122 for a pH meter, so I can constantly monitor the pH, as I am lazy and don't like to do testing any more than I have too

.