[MikeP]

So I bought this test kit and I have used it twice so far. The first time I used it was on Aug 8th, I got a reading of 500 but was expecting to see between 400 and 450. I figured 500 was possible if the old kit (instant ocean brand) was screwy so I didn't think to much of it. I did a 20% water change last night and now I wanted to get on track with maintaining calcium at about 450. So I tested with the salifert kit again and now it's giving me a reading of over 500. This is impossible right? I've added nothing to raise the calcium since July 30th and with the last test in my old kit I got a reading of 480 on July 31st. I thought I would see where I'm at now and then start a calcium maintaining procedure. So the big question is... am I reading the instructions wrong or is this kit faulty? What are the salifert kits generally like?

Thanks for any advice

PS the calcium "load" in my tank should be quite low, I don't have to much for LPS/SPS yet and there is a medium size clam in there.