Test kits can be a bit confusing, that's for sure. I use Red Sea Pro to test Magnesium. I used to use Salifert kits to test for Alkalinity and Magnesium, but now use Hanna Checkers for those. I had what I thought was Briopsis, and was attempting to treat it with Kent Marine Tech-M, and that's when I bought the Red Sea Pro Mag, Nitrate, and Phosphate kits. With the Nitrate and Phosphate kits, once the color change had occured, I simply had to read the amount of reagent left in the syringe. The Magnesium kit was backwards, and I had to read the amount of titrant
used. Naturally, when I first started using these kits and was in a hurry to test all three, without refreshing my memory by reading the instructions, I'd mess up on the Mag test. There was a stretch of time when I was baffled because the more Magnesium I added to the tank, the lower my test results were. My target level for Mag was 1500-1600 ppm, but before I realized my error(s), the Mag level in my tank was 2000 ppm. Long story short, it turned out to be hair algae, not briopsis, so the Mag did nothing to it. I burned my mistake into memory, and haven't messed a test up since then. I learned that Mag can be raised rather quickly with no adverse effects, so you don't have to resist the urge to move it up to where you want it...
PS: The bottom flange of the plunger is your indicator when it comes to syringes. When I say bottom, I'm referring to the end of the plunger that faces the "needle". Rubber or plastic, the lowest part that breaks away from the wall of the syringe is what you use to measure with.
The test kit i use for calcium is part of the API saltwater test kit. However I was wondering about the pinkish algae right in front of the Halimeda.
You really should get a better test kit. Just saying...
The pinkish algae in front of the Halimeda... (first sentence, post #8) gracilaria.