Growbed with hydroton enough for filtration for DWS?

[BenHehle Beamz]

Hi,

My plan is to install a 1000 l IBC tank with overflow to a media grow bed and then to 4 floating rafts. Is it enough for filtration or should i install a swirlfilter after the media growbed to filter all the solids out? Any recommendations?

[Vlad Jovanovic]

Thanks Chris

Airlifts seem like a really keen way to move water around in certain settings, and I'm interesting in learning more about how they'd be applicable in the future. Right now I'm trying hard to not bite of any more than I can chew, and it's just me and the Mrs. doing all the digging/building/plumbing etc...

Thanks for the heads up on the stocking density. I was planning on posting my (planned) stocking numbers for some feedback. As it stands I figured a bit under 200lbs of fish roughly. (I figured I might need to add/remove fish according to what the nitrates tell me) This figure is based on modifying Friendlies minimum recommendations in their manual after some toying around with Dr. Lennards calculator, and some plain 'ol guess-timation based on other reading. It's very encouraging to have you confirm that I'm in the ball-park somewhat. 

Chris Smith said:

Great system Vlad!  I am playing with airlifts to get clean water to towers and NFT instead of pumping. I agree that many overstock their systems. In my integrated systems I am trying to stay at a low stocking density of .3 lb/sqft. In my big tank that is very difficult though due to the size of the tank.

Bill there is a discussion in the raft/deep water growers group addressing your questions.

[Chris Smith]

When dealing with larger tanks it does come down to guesstimation because it is not good or easy to weigh the fish on a regular basis. Whenever I net at my fish they get a little freaked out for a while and sometimes I damage one that later goes belly up. For larger systems it is important to have good solids removal so you can guestimate the fish load but if you have too many pounds the solids are not an issue. The fish are constantly growing so your poundage is always on the rise too.

In my 1000 gallon tank I have to put on a mask and actually dive the tank to get my guestimate of poundage. I do have an idea when I am way over by the solids in the gravel beds. I have to dive the tank this weekend because I know I am overloaded and need to sell some fish but I'm not sure of how much I can spare yet.

[TCLynx]

This is an interesting topic, the number of fish or weight of fish vs the amount of filter/plants.  My first few years I probably ran a stocking level much higher than needed because of pH issues holding my plants back.  Now this past winter I've actually experienced a lack of nutrients in one of my systems for a while.  It can be a tricky balance.  Like so many things in aquaponics, it depends.

[Trevor Johnson]

Are there any ratios of fish stocking densities, media bed sizes, or the like to scale up the system?

Would you stop the system just for the raft beds? Or would you stock the system for the raft beds plus the media beds? I assume you're growing in that media beds/biofilters.

Do you still have a settling tank just in case the beds get Filled with solids?

[TCLynx]

I don't know if anyone has studied enough mixed systems for long enough to have really solid stocking rules yet.

I generally go with the low density stocking recommendations for each type and add them together.

So if a 4' by 8' at 1' deep media bed can support 32 fish (assumption being they grow out to 1 lb each)

and

a 4' by 48' raft bed can support around 60 fish by low density standards

Then a mixed system with those two beds might support 92 fish that grow out to one pound each.

I don't know how well a single media bed will handle all the solids going to it long term so a settling tank to catch the larger solids might be in order.

I prefer more media beds (6-12 of them) to spread out the solids and spread out the gunk a bit and I sequence the flow to them to allow the worms time to work on the solids and avoid the slime buildup where the water enters the bed.  I also like to have perhaps only twice as much raft as I have media bed instead of 6 times as much raft so that the solids build up is less likely to become a problem and the settling tank may not be needed.  And collards and kale have been my best sellers and they are big enough plants/longer term plants that I find growing them in media beds seems to work better for repeat long term harvesting.