Cycle timing

[Sylvia Bernstein]

If you are growing using Flood and Drain on a timer, how often to you cycle and for how long?  I think most of us use 15 minute interval timers, so I'm guessing that the duration of a cycle is typically 15 minutes - I know mine is.  I tend to go 30 minutes between cycles if everything is nicely balanced and only 15 minutes between if I'm overstocked with fish and need the oxygen more than the plants need the dry period - which is where I am in 2 out of 3 of my systems now.  The other data point I have is Joel at Backyard says he typically goes 15 on / 45 off with his systems. 

What do you do?  What have you found works best, and what just doesn't work?

[Sylvia Bernstein]

Hmmm....I've been working with Hydroton for many years as well and have never noticed this.  It is essentially a porous rock, and you typically don't see capillary action in rocks.  I'll try an experiment with the net pots, though, and see if I get the same thing.  The top layer of my grow beds stays completely dry.  That said, there could be environmental differences between our environments that are causing a difference.  I live in a very dry, high altitude climate.  You and TC are both closer to (or at!) sea level in humid environments.  Maybe this is causing a difference?  Interesting.

[AJ Grottke]

Sylvia the environment could be causing a difference.  I will take photos of some hydroton that is wicking for you, and put them on.   I even have a DWC tray that has the net pots above the water line (its not in a raft) and the airstones in the tank spray enough water into the air to moisten the hydroton in the pot, they are even touching the water!

[TCLynx]

The wicking effect of hydroton is minimal, I wouldn't count on it to lift water more than an inch or so normally.  Perlite , vermiculite, and probably a few other things can probably wick moisture higher but still wicking stuff should be thought of more as an offshoot type add on for aquaponics, not depended on for the main filtration.  I would think of it more for seed starting and experimenting.

[Robert Pugh]

Hi All-

Just joined and happy to see so much interaction on this forum!

 

I just completed the mechanical assembly of my first test system.  It is tiny at only 10 gallons. It took some tuning of the bell siphon to get it to cycle consistently, but I learned a lot and figured out some of the quirks. The flow rate into the grow bed is just a trickle, but because of its small size (less than 1 gallon of water when filled with media), it fills in just over 2 min and drains in just over 1 min. Turning down the flow causes equilibrium issues at various points in the cycle.  I've come to the conclusion that the only way to slow it down would be to switch the plumbing to smaller diameter. I'm currently using 1/2 PVC.  I don't know of easily available plumbing smaller than 1/2.

 

So the questions:

- Is my assumption correct that you can only slow the flow rate so far for a given diameter standpipe?

- Will anything grow if the roots can't dry in between cycles?

- Since lettuce can handle NFT, might that be a good choice for my setup?

 

Thanks in advance for your answers.

[Harold Sukhbir]

Hi Robert,

Yes you're right, diameter of tubing has a major role for both in flow and out flow. There is a smaller diameter PVC called CPVC, used for hot water application which can be used for bell construction. I would assume you can reduce your flow rate by at least 75% of the present value(of the 1/2") with the smallest diameter CPVC pipes. I've also run constant drip(wet roots) for a wide range of plants with no rotting/dying issues. Yes you can grow lettuce in water but wouldn't you like to grow other plants as well? If you decide to go with the smaller pipes and reduced bell size, to avoid clogging, it is suggested that you don't permanently glue the joints together but press fit so that they can easily be removed for periodic cleaning.

[TCLynx]

Plenty of things will grow even with such short cycles.  There are people who run some constant flood beds and as long as the flow rate is enough to keep the water flowing through the bed well oxygenated, it can work well for most plants so I wouldn't worry too much about your fast cycling at this time.

[John Cubit]

This seems to be an ongoing issue.  I have been searching here for a few days and I still can not find a suggested fill vs.drain rate.  I put together a small 10 gal tote on a 20 Gal tank.  I set it up with a 1/2" cpvc feed line with a ball valve and put in a 7"  bell siphon 3/4" drain on 9" Hydrocorn bed.  Thing is it drains in 33 seconds, takes only 3:53 seconds to fill.

What is an acceptable fill to drain rate?

[Robert Pugh]

On this forum, I've found a lot of suggestions round 15 minutes for the full fill drain cycle. I kept my 2-3 minute cycle for many months with no luck whatsoever. Plants wouldn't start from seeds and transplanted seedlings would just stall at about an inch tall. I tried basil and spinach mostly.

I recently replumbed with a smaller diameter plastic tubing and increased my cycle to 11 minutes. So far so good...seeds are starting and seem to be growing quickly. Even the basil that refused to grow before seems to be taking hold. I think I have to attribute this to the longer cycle time. It's only been a couple of weeks since the rework, so time will tell, but it looks promising.

[John Cubit]

I have had it as high as 20 minutes but then the siphon fails to start just trickle. Steady mix is a fill in 5 minutes, drain in 35 seconds.  I have tried a shorter bell but didn't change anything.  Shortened downspout, no change. 

 Now as for the water feed that is on 1/2" cpvc with a ball valve on a 450gph pump.  I can not get smaller but I can go to 3/4".

Mind you I know the tote is small it is for testing 4 Ornamental Thai Chili plants and seeds, this is a 20 gal tank with a 10 gal tote.

 

[Robert Pugh]

I had a similar experience with adjustments to flow rate into the grow bed. There was only so much you can do with that. Several tweaks made the start and/or stop of siphon marginally more reliable, but never lengthening the cycle time by much.

I came to the conclusion that the only way to increase the cycle time is to reduce the diameter of the pipe out of the GB. I left the 1/2 pipe in place and ran a 1/4 plastic tube inside it. I used hot glue to hold the tube in place at the top of the stand pipe. I already had a tee and a ball valve coming off the pump to control the flow, so I adjusted it to just barely a trickle. The siphon worked on the first try and hasn't failed since. This change took a total of 5 minutes and increased cycle time from 2 to 11 min. It also seems to have increased the reliability as well.

I can't tell from the picture where your ball valve is to control your flow. Just make sure it isn't inline restricting the flow. Instead use a tee to allow excess flow run back into the fish tank.