Could you be overfeeding the fish? I had that habit and phosphates were high, I got cyano
. It's better now with less feeding.
Do you have a pic of the sand and cyano
? When I had it, it had a habit of collecting tiny air bubbles all over it, so I knew it was cyano
. If your tank is new, it could be diatoms, "new tank algae", but with that phosphate level and the deep red, sounds like cyano
and the high phosphates are likely the contributor.
As for the Mag 7, I don't know how much flow that is, but I have two Maxi-jet 1200s in my tank and my lfs
says I need at least one more. I have a 55G also. You might want to get anoter powerhead and put them one on each side of the tank, pointing upwards towards the middle, that way you'll get flow in both directions and hopefully eliminate any dead spots.