Welcome to RAG!
Your water can check out good, but you can have a lot of nitrate and phosphate "locked up" in the sandbed and LR.
You mentioned that your sandbed was black. This is one major area to check into. Usually a sandbed will not all turn black unless there is a serious problem. You may see some dark areas though.
How deep is your sandbed?
What is the material used?
What is the grain size of the material?
Directly related to black sandbed is feeding. Over feeding is a major problem and cause of cyano.
What is your feeding schedule?
Are you useing any liquid foods or other additives?
Yes, lighting can have an effect on cyano (red slime). Old bulbs don't produce the same light as new ones. Usually you want to replace PC bulbs every 12 months or so.
Cyano thrives in dim light.
What kind of lighting are you using in the tank? (size (in watts), type, and color of each bulb)
Live rock is also a factor.
How much live rock do you have in the tank?
Filtration is a large factor in cyano control.
What is your filtration system?
What is your cleaning schedule for it?
Do you have any other power heads for additional circulation?
As you can see from my previous posts, I'm not a big fan of EM or other chemical controls for cyano. I suspect your ammonia spike was because you killed at least some of the existing algae.
Your clean up crew of snails and hermit crabs is small for the size tank, but don't change that now. Most don't eat cyano, so get the cyano problem under control first.
Well, I've got about 10 questions for you. Let us know what you are doing, and I think we can give you some advice on how to get the cyano under control.
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