To drift back to the OP's question... One of the big things I look at in an algae wafer is the bulking medium. A lot of companies use wood ash to increase volume and give the wafer some structure when it's pressed. Nothing inherently wrong in wood ash, I just prefer not to put something quite so acidic in my tanks. The only wafer I've found with zero wood ash is wardley wafer. My plecs like it, but their line of shrimp pellet falls apart too fast. Check out the ingredients on your package. I've seen that brand here and there, but never really examined it closely.