The instructions for dosing Excel are on the bottle. You dose a major dose at each water change, then dose about 1/4 of that dose every day or every other day. Seachem does not acknowledge that Excel does anything to algae, so you wont find anti-algae dosing instructions on the bottle. Some of us dose double what the bottle says, some dose 1 1/2 times what the bottle says, and Tom says to just do as the bottle says. The choice is yours. The bigger the dosage the more likely it will harm shrimp and certain plants like vals and anacharis.

Your GH is either 5.6 ppm or 5.6 degrees of hardness. The former is low, the latter is normal. If you feel you need more magnesium or calcium, use GH Booster or Equilibrium per the bottle dosing instructions.