Question about growout

[cdipasquale]

My picasso babies are about 50 days old now and every once in a while one will start hanging out on the bottom, not eating and breathing heavy and will die within a few days. I have lost probably 8 of them over the last month from this exact same thing. They do seem to be the smallest, skinniest babies. The are in a 150 gallon growout system, their cell is about 12 gallons.
Ammonia 0
Nitrites fluctuate from 0 to .5. I'm setting up a bioball tower this week to help with this but I make sure to not let it get over .5 right now. I just have rock rubble in the sump right now and it isn't keeping up.
Nitrates <20
Specific Gravity 1.023
PH 8.3

So my questions are: Is it normal to have a little die-off of the weaker fish? Should I be seperating the smaller ones so they can feed easier? Is .5 nitrite enough to cause this? Or could something else be going on?

I wasn't worried at first because I just lost one here and there but at this rate, by the time they are big enough to sell, there won't be any left.

 

[jbax]

do you see him getting picked on? how many are in each cell?

just pluck him out of his batch and put him in a younger batch. sometimes after a while the weaker/smaller ones will be singled out.

 

[cdipasquale]

I don't notice them getting picked on but I don't get to watch them constantly, so maybe. There are only about 50 in the cell so there is plenty of space for them.