The AP tests are usually fairly reliable. If I’m not 100% sure of a reading (like getting a 0 reading) I’ll use half as much water but the same about of drops to see if I get any color change. I think I read that they can expire with time so if they are old you might want to have a
lfs test it as well.
Using the Phosguard I haven’t noticed any appreciable drop in
ph or
alk and is states it doesn’t leach back into the system so I usually leave it in for a couple of weeks at a time.
As long as you vacuum the
cc it usually isn’t a problem.
Just about everyone has algae issues at one point in keeping a sw tank and it’s not always tied to
po4, that just seems to be a culprit most of the time along with excessive lighting\feeding.
Are you talking about a few patches here and there or is your tank inundated with it? I have 0 readings as well with two different tests and I still get small patches every once in a while. I think high levels of
no3 can bring it on as well but you have to have readings of over 20
ppm for that to be a factor and most people don’t.