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Flood & drain beds starving, but float tank doing well ... why?

I am running a fishless system, it just completed cycling about a month ago and now some issues are becoming apparent.

The short story is that my plants in the flood and drain are starving, while those in the deep float are doing well enough.

My setup is that the water is pumped from the holding tank up through the deep float tanks, which overflow into the flood and drain tanks, pump runs just long enough to flood them, this cycle is repeated every 4 hours between 6 am and 6 pm, it doesn't run over night.

In the float system I have mostly stray cabbage seedlings and lettuce, also a few spare carrots and one beetroot that were more or less guinea pigs while the system cycled. In the flood and drain, which is now half full, I have lots of beetroot seedlings coming on.

The beetroot in the flood and drain are obviously starving, they are slow, dark purple, and yellowing older leaves. The only ones that are looking any good are the few around the actual overflow pipe where the water flows into the bed.

In contrast, the extra plant that was put in the float system at the top is green and looking pretty good, and the seedlings from the same batch that are still grown in standard soil gardening are doing even better.

The youngest seedlings planted in the next flood and drain tank down the line are simply not doing anything at all.

What do you think the problem is here?

Should they be flood cycled more often?

Should I add more nutrient? Right now its showing 50 ppm nitrate, does the flood and drain need a richer nutrient solution than the float?

Do they need to be completely separate systems, the flood/drain and the float tank?

Or should I restructure the whole thing and have the flood and drain boxes first in the cycle, draining into the float tank? (this would need serious rebuilding from scratch)

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Another idea ... what if I made the beds stay flooded longer?

Right now I've got them always draining slowly, it takes about 3 1/2 hours.

But I could rig up a washing machine solenoid and have them hold that flood for 2 or 3 hours, then drain quickly.

Would that help?

A good time to shoot for as far as flood and drains cycle is one cycle every 20 minutes or so.

The long time between your cycles, as well as not running your system at night might be stressing out your media bed plants. This is a soiless environment, so your plants will need water more often because your media doesn't hold water the way soil does.

More than likely it is the bacteria that are not flourishing in a Flood and Drain that is stagnant most of the day. 3 1/2 hours that the plant roots have limited access to oxygen will stunt growth too. Bacteria and plants want the water constantly flooding and draining providing food and oxygen for them to create nutrients for the plants. Think of the flood and drain beds as lungs and you are asking them to hold their breath for 3 1/2 hours. You also said this is a fishless system, are you only supplying ammonia to your system? Plants need 16 different nutrients to thrive and usually fish food has these nutrients.

Hmm ... every 20 minutes could be a problem, there's simply no way they can drain that fast I think.

But I will step it up as fast as possible.

I'm not sure how fast they can drain, I will have an experiment and see. I'm guessing it may be about 40 minutes.

If all else fails, I'm thinking of running them as constant flooded beds, but with the media in there still, and introduce a lead from the bubbler for oxygen? Never heard if that being used but I don't see why not ... would it work do you think?

I'm adding plenty of other nutrients as well as ammonia, p/k are in there, and we also add seaweed, iron, lime ... no deficiency signs in the raft end of the system.

Air is the biggest issue your having.. notice the plants next to the incoming water are doing the best,, its the only part of the media bed that has enough air..

the water should go through the media beds, then drain into the raft and back to the tank.

50 ppm should be plenty nutes to grow anything you plant..

with the right size plumbing you should be able to drain your beds as fast as you desire.. what size pipes are you using?

a ten minute fill and 15-20 min drain are pretty standard... regardless of system size, your pump and plumbing should be sized to allow this.  my guess is the plumbing is too small.

maybe post a picture of the system?

I flood each of my grow beds every hour, and have had very good growth in my system.

Rob's point about draining from the flood/drain bed into the DWC bed is an important one.  You don't want your solids settling in your DWC beds.

If you have a good solids filter this is less of an issue, though you'll certainly want a lot of aeration in your DWC bed in this case.  UVI found that their plants above the aerators grew much better than the plants between aerators.

Ok I've timed it.

With the system on full drain it takes 30 minutes to pump the beds full.

It takes 90 minutes to drain completely.

If I shut off the drain during the pump cycle, I could get the fill down to about 13 minutes.

If I drained the 4 tanks through 2 pipes instead of one I could halve the drain time to 45 minutes ... but the problem is if I was to do that I'd need to use 2 solenoid setups to shut off the 2 drains ... and I only have 1.

Shutoffs for the drains would be an absolute must, no way would the pump ever be able to fill it otherwise with 2 drains running full.

Theoretically, without massive changes I could lower the drainage time to 22 minutes, but that then needs 4 solenoids ...

Right now I have it reset to cycle as short as possible without changes, that is every 2 hours, during the day, but my timer can only handle 10 on/off programs per 24 hour period so I had to spread that out to 3 hours during the night.

To speed that up any more I'll need to get a new timer capable of a lot more cycles, I've no idea where from, but I'm not in town for a couple of weeks so by then I should be able to see how the plants are doing with more cycles.

The drains are standard garden hose size, out of each of 4 half drums. However currently those all join into one hose to drop into the holding tank.

The pump is 15w, labelled capable of 900lph ... and I don't want to go any bigger than this if I can help it, being on alternative power, I would convert to entirely DWC and forget the carrots rather than have to use a noticeably bigger pump.

ah.. a lot of what not to do.   sounds like a rebuild is in your future.

Yeah, your pipes are simply too small.  There's no way around it.  Even if you put in 4 drains you'd still get clogged eventually.  For my old half-barrel setup I had 1" drains flowing into a 1-1/2" main drain.  

You can flood every hour with one of those old non-digital timers.  Many of them have triggers every 15 minutes.  Or you could take two 20-cycle-day digital timers and put them in parallel.

Instead of solenoids, you could just use bell siphons.

I am runnig a humonia system or fishless system, I would like to share my experience, I designed my growing bed also is the biofilter in such a way to have two inches of nutriens at the bottom of the bed is circulating continously, the medium I am using is a mixture of small gravels and clay balls, depth of medium is 6 inches, I add iron and potassium besides the urine to my tank and it seems doing good job in growing healthy plants. The top of the medium is constant moist, the roots have enough oxygen to breath and water plus nutrients to absorb. Nitrifying bacteria and red worms are surviving and converting urea, ammonia to nitrate.

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