I tried eco and FSS and seemed to have a weird effect. FSS releases tannins, humic acid, etc to help lower the pH. Eco has a high CEC and absorbs everything in the water and I think between the FSS releasing and EC sucking everything it can up, it didn't do much for my buffering once I mixed them. I would try and get more FSS if you plan on using it for it's buffering.
20g platy, , 2 x 10g shrimp, 3 x 20g shrimp, 7.5g shrimp and 1 great dane/mastiff puppy.
Sump Pimp #2
My Tanks and my shrimps