i buy the 15 lb bags at Petsmart.. it's big chunks, so it doesn't bring your PH up as high or as fast. i put one bag in a 55 gallon tank.. in the 210 there are probably 2 or more bags worth mixed with black gravel and river rocks (we combined the substrate from 2 tanks when we started up the 210).
the substrate for the 180 is the same.. the rest of crushed coral/black gravel mix and the crushed coral/ river rocks mix from the 150. that is probably 2 bags worth of crushed coral also.
the substrate for the 180 is the same.. the rest of crushed coral/black gravel mix and the crushed coral/ river rocks mix from the 150. that is probably 2 bags worth of crushed coral also.