black foam board works good
i blacked out my tank using the black foam board in the school supply section at wal-mart it also helps insulate the glass a little, i did both sides, 3/4 of the bottom and the top and used an aquarium background on the back. on the front glass i made a black curtain that has magnets to attach it to the screen top
it is not necessary but it helps keep them calm down while they settle into their new surroundings .
Re: How to black out a tank
no its like 2.88 a sheet and if i remember right i think i used three or four sheets to do two 20 long tanks. the backgrounds vary on price i got mine for 6.99 on sale at petsmart.
Re: How to black out a tank
I used aquarium background from a pet store just for the look but just about anything will work :)