Bioguard super soluable is Di-Chlor powder. But what were the other chemicals they told you to add?

Just so you know, the only things you should worry about with a green pool is pH and chlorine levels (I'll bet they sold you calcium carbonate, too, useless in vinyl pools).
You did say your CYA is currently 51ppm, didn't you? That means you need to shock your pool by adding chlorine till FC reads 15ppm.

I'm wondering if your FC is actually high and is bleaching out the test strips and the pool store's test, probably DPD.....

Try using an ordinary, cheap OTO test kit. If the chlorine test side is clear, you have no chlorine. But if it's yellow, orange or brown, you have LOTS of chlorine and it's bleaching out the other tests.

Carl