Have you tested for phosphates?
Don't worry, you will get through it. Other than being an eyesore it won't hurt much unless it takes over your coral which would be an extreme case.
GFO may help.
A reactor with carbon and GFO is cheap and worth a try. bulkreefsupply has a nice one for 60 bucks.
But if the $18.99 is a bit too much for the red slime remover, $60 may be over the top.
If you decide you want to use the red slime remover, I have some you can have if you PM me your address. I used it on my 125 gallon and it worked great. All my LPS, SPS, and fishes are doing great and slime is gone. I have enough left to treat about 100 gallons.
Aaron