How many in the grow out is too many??

Hi guys, I'm looking for some advice on my grow out tank.

The tank is 3'x1.5'x1.5' and my filtration is handled by 3 sponge filters each rated to 100L as well as a small power filter that runs at 500L an hour (this provides a nice current in my tank).

I currently have 2 relatively large spawns (approx 200 in total) in there growing out from last month (2 of my 3 Breeding pairs gave me a spawn each at the same time) with 2 small adult males (~8-9cm) and a female (~10) and all is well.

I ask because one of my pairs in another tank laid again last night and they regularly give me large spawns of around 100 so these will go into the grow out in about 2-3 weeks time. I do have some more of the same sponge filters in the shed for my next tank but I haven't bought that yet.

My question is at what number will the fry overload my filtration system in people's opinion from experience?

I also do water changes at 10% per day or 20% if I miss a day, then 50-60% every couple of weeks to ensure nitrates aren't creeping up.

Thanks for you replies in advance guys.

for stability get a big canister on there. the sponges will not be able to handle the bioload and internals are near on useless for biological filtration.

in its current setup you will run into troubles with the current stocking levels as the fry get bigger. I use a standard 4ft tank for my growout tank and it runs a 2200l/h canister plus UV and 3 sponge filters plus extra bio-balls floating around the top. i like to keep it to about 500 babies in there.

Thanks Doug, might have to source a cannister filter then as it sounds like a good idea for sure

I had a 3'x15"x15" tank at one stage with 300 fry in it. All between 5-10cm (the odd one over or under)

The tank ran 2 internals and 3 corner filters. Water changes twice a week.