I would Say one, but break it in half, they are scavengers, try putting in right next to them when you turn the lights off, This would stop most the other fish eatting it a little bit, can be alittle bit tricky, ( sorry about spelling)
i have 2 catfish, 3 algae eaters and 2 shrimps to do my cleaning around the tank..the shrimps have cleared all algae on my bogwood in a day! but what i do is fire 2/3 wafers into different places...the fish go for one and the two get ate by them fish.
