Don't get too wrapped up in ppm values specifically, test kits even when properly calibrated are estimations at best. Keep an eye on plants, fish and algae, they are the real indicators. Most algae issues are due to CO2 probs, whether just not enough or inefficient circulation. I think a small amount of GSA is probably normal and virtually unavoidable, I clean a little off my glass every 3-4 weeks, just kinda part of the deal. GSA on leaves, however is indicative of less than healthy growth, so watch for that. Sounds like you're on the right track though!