Refractometer or hygrometer "HELP"

Yes I'll will be getting a phosphate kit soon, and I will be doing a water change this weekend. I've never tested for phosphates before and I just use tap water I've never had algae problems before and I heard that what phosphate does or am I wrong?
 
Yes I'll will be getting a phosphate kit soon, and I will be doing a water change this weekend. I've never tested for phosphates before and I just use tap water I've never had algae problems before and I heard that what phosphate does or am I wrong?
phosphates can stunt coral growth as well...and tap water will almost always have it in there.
 
I have the aquarium systems master test kit by instance ocean but it's getting old and the dates on the packets are going to run out soon, what test kits do you recommend?
 
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