gallons

Hi. I have been looking through the internet at ways in which to calculate the stocking of a aquarium, and different methods have given different sizes. For example one method says about a tank 185 liters while anothere method gives the answer of 300 liters. So the stocking that i was using is...

I have a 26 gallon tank with driftwood and a few live plants   i currently have.. 1 albino cory catfish 2 platies 1swordtail 1  black phantom tetra   can i add a school of cherry barbs and an angelfish?   im looking to transition to a semi aggressive tank