You will need to cement the concrete blocks together and connect them to the floor. This would cause permenant damage to the floor. Try a premade stock feed tank that will just sit on the floor, yours for $500 and would be able to get one up to about 2k gallons.
If not rubbermaid then I'd stick to a wooden build.
If not rubbermaid then I'd stick to a wooden build.
and then after you have like 20,000 guppies put the fish in
. Feeding Frenzy
.