I have just started using equilibrium (thanks to this forum) in my 38 gallon tank with ro water. The bottle instructions (seachem) says to use 1 tablespoon for every 20 gallons, when setting up aquarium or making water changes. I have been changing 50% water so 20 gallons and using 1 tbsp. Now I am wondering if the instructions mean 1 tbsp for 20 gallons of new water that is added or is it 1 tbsp for 20 gallons of water in total, which would mean I would need to use 2 tbsp. Any suggestions are greatly appreciated.