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I'm wondering how people harvest their growbed but maintain their biofilter.  

I've got a new IBC AP system.  FT about 200 gallons, GB about 75 gallons. Standard build, cut off the top, flipped it over, constant flood.  Started with 30 2 inch golden tilapia and a handful or lettuce seeds.  I've eaten about half the lettuce and the fish have more than doubled in size.  I threw in some spinach seeds, but at the rate I'm going, I'll have nothing significant growing in my growbed and 30 5 inch tilapia in my system.  Seems to me, by the time the seeds from the next crop get going, I'm gonna risk some fish death.

How do people manage this sort of thing?  I'm thinking I need to remove some fish as they get larger for starters, but what I'm really interested in is how people harvest yet maintain a bio filter for the fish.

Thanks for helping a newbie!

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I have 3 stages for my plants. I start seeds in starter trays then when the plant is about 3 inches tall it gets moved to a constant flow raft bed then to my grow beds. That way if I lose a plant I have a small one to pop into the GB so the cycle maintains itself

from one newbie to another (in other words I'm not an expert)--that's really encouraging news! 

If it were me, I'd leave a few big lettuce plants in the growbed. Maybe even to get a harvest of seed, which will save you about 79¢ for the next round of homegrown salad.

The grow media will continue to provide biofiltration without plants. The nitrates that the plants used will rise but you can probably just cut back on your feeding to manage it until your new plants get established. Worse case you might need to change some of your water to bring the nitrates down.

I thought about that a year or so back, and decided to grow swiss chard to take care of that. It gets cut back frequently but as long as I leave one small shoot, it comes back very quickly. So, I harvest my lettuce etc..leave the chard in and never worry about nitrates getting to high.

Hi Gary,

You need more GB's for that amount of fish orr you need less fish.  A 75 GB is approx. 10 cu. ft. The rules of thumb is a maximum of 1 lb fish per cu. ft. of grow bed space. This would mean within 6 to 8 months you would have 30 lbs of fish, which will be 3 times the amount you'll need for that size of GB. If you harvest 20 lbs fish within/during that six to eight month period you'll be OK. You may get away with harvesting less(but not much less) than this amount as you do have a very large FT. You can cut lettuce at the roots a few times and they will regrow themselves, this way roots remain in the system. BTW you'll be surprised how little you can feed fish and they survive and thrive!  Although I love to give them all that they ever need and then some more

Thanks for all the feedback.  Yes, I am worried about the fish load as the fish get bigger.  I started with a barrel system and my GB and FT were same size.  But when I followed the IBC instructions I found online, it lead to a smaller GB than FT.  Always thought that was a little odd.  I may try to run another pump and add a growbed, not sure.  

Thanks again everyone for the ideas.  Next time I'll grow different plants that I can harvest at different times as well.

Good thinking Jeffrey, we might need the dollar even more next season! :)  And if I am following your thinking here, perhaps plants that are heavy feeders could be used too "Cucumbers for one are heavy feeders"
 
Jeffrey Ihara said:

from one newbie to another (in other words I'm not an expert)--that's really encouraging news! 

If it were me, I'd leave a few big lettuce plants in the growbed. Maybe even to get a harvest of seed, which will save you about 79¢ for the next round of homegrown salad.

Gary if I understand the short of your question it is to maintain a healthy bio filter between seasons.

I don’t think we lose the healthiness of the bio filter “Grow Beds” if they remain wet and the water is circulating in the system as normal even with a high density of fish.  The grow beds will continue to filter even with few plants, just like a wet/dry bio filter on a reef tank, as long as the ammonia level is in check.  I think the fish would remain healthy as long as the water chemistry was managed.  Perhaps the real trick is to have enough fish waste “nutrients” to maintain plant life.

Start some tomatoes maybe.   Just one newbie to another.

You always could through in some garlic.. They're heavy feeders too, and take a good while to develop. Or even onion.

This is what it looks like.  Since it's on top of the IBC  FT, it's sort of high.  Do you think I could add a tomato in the corner and it run over the side?  Cause if it goes up, it will be too high to harvest.  Not sure how to make it so the vine doesn't get cut or bent over the side though.  I like the idea of leaving a tomato plant in there so while the next round of seeds germinate, I at least have a heavy feeder still working.

This is the actual system.  See how tall it is?  I should have dug the FT down some.  Yeah, too much FT, not enough GB, live and learn :)

Cut a length of 1 1/2 or larger pipe to act as a guard. Put 90s on the ends with pipe long enough to hold the guard pipe high enough above the edge to protect the vines.

Gary Wong said:

  Do you think I could add a tomato in the corner and it run over the side?  Cause if it goes up, it will be too high to harvest.  Not sure how to make it so the vine doesn't get cut or bent over the side though.  I like the idea of leaving a tomato plant in there so while the next round of seeds germinate, I at least have a heavy feeder still working.

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