I was wondering today if everybody calculates the "actual" amount of water in there tank. By this I mean if you have a 100g tank, obvisously there is not 100g due to all the room sand/rock/etc take up. So, if you're doing a 20% water change, will you swap out 20gallons or a bit less figuring that 20% of the actual water may only be 15 gallons.
The same goes for dosing medication. If the directions say use 1 tablespoon for each 5 gallons, I"m assuming they mean the "actual" amount of water in the tank.
Anybody know of a rough way to calculate this, I swear there was a calculator somewhere but I cannot seem to find it