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How deep is too deep?

Hey,

I'm in the process of up-scaling my mixed media system. I've recently found some large 500g tanks that were constructed by someone who used to own a hatchery business. The price is great and there are several tanks available. The dimensions are 8' long x 4' wide and 2' deep. Ideally I would be using some of the tanks as media beds and others as dwc's.

i'm about ready to pull the trigger but I'm concerned about the depth. I know that conventional aquaponics design calls for beds (both DWC and media beds) to be around 12" deep or so. Is the 24" mark too deep?

If so, why? Aside from the added expense of the extra media,I cant really think of any negatives, so long as Im able to adequately circulate all that water. Any other reasons that this might be a bad idea that Im missing?

Thanks in advance.

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Replies to This Discussion

Permalink Reply by Chris Smith on July 21, 2012 at 3:14pm

24" in not too deep for DWC or media in my opinion. The biggest concern with deep beds is the weight of water. I prefer to elevate media beds and small DWC troughs. A 4x8x24" deep bed will hold a lot of water in the voids of the rocks so if you elevate them you will have to build the bases strong enough the handle the weight of the water and media. Water weighs 62.4 lbs/cubic foot or 8.3 lbs/gallon. A 4x8x24 DWC trough will hold 58.6 cubic feet of water when filled 2 inches from the top. That is 3660 pounds of water!!!!

Permalink Reply by Sahib Punjabi on July 21, 2012 at 4:37pm

Hey Joshua,

24" deep for media bed or DWC is as Chris Smith writes, be careful about the weight. During a recent visit to TCLynx new farm I witnessed a number of such deep media beds. She informed me that she uses them for some large plants/trees and they also provide excellent filtration.

Love to see some photos when you set them up.

God bless,

Permalink Reply by Josh on July 21, 2012 at 5:09pm

Thanks for the responses.

. In my design the dwc will be on the ground and will also double as the sump. So in this case, the added depth of the water will be an advantage, The water will pump into the FT (the system's high point) from the DWC, and then the FT water will over flow into the media beds. Finally the media beds will drain back into the dwc. I'm trying to use as much gravity flow as possible, so the media beds and the Ft obviously will have to be raised.

The weight is certainly a concern, but I have a bunch of cinder blocsk from my current system that I plan to use.

Is it possible that the plants might be able to be more densely planted in the deeper beds, as the roots will have more room to grow in the greater depth?

Permalink Reply by David Stoneburg on July 21, 2012 at 11:08pm

Joshua - another nice thing about deep DWC is the opportunity to diversify your fauna, put some crayfish, clams, mussels, prawn, etc in the bottom to help with cleanup.

With the pump taking water from the sump, the water with the least particulates, use its head to pump up to higher growing areas. This could be nft gutters, vertical (strawberries, herbs, lettuce) tubes, aeroponic cloning misters, ...

One of my favorites is to pump it up a plastic "tree" to feed several horiz. grow tubes (add a 1/4" soaker hose air line on the bottom and it can work as an aeroponic cloner as well as giving full size plants the extra root zone oxy they need) while the drain goes into the main tank helping to oxygenate the fish water.

Even though one of the nice things about any kind of hydroponic garden is increased production, plants still need light and grow space. For example; a person can grow lettuce under indeterminate tomatoes as they don't need direct sunlight and their growth cycle is shorter - staggered plantings means months of great salads. Being a cool weather crop means the lettuce production will last longer than the sun loving tomatoes.

Sahib's reply about providing great filtration only applies if the effluent is spread over the media or you're doing a form of ebb & flow. If you only use one pipe drain for a single input zone, and depending on how high your exit plumbing is, that is your filtration zone.

As far as growing larger plants go, yes deeper is better, they need something to keep them upright. But the rules about canopy space still apply, plants need certain amounts of light. Most people I've heard of who grow dwarf fruit trees in water based systems spread them out in buckets or half barrels.

Please pass along what you have decided and pictures of the finished product.

You are only limited by your (and our) imaginations. Ahh, networking, brainstorming - synergy!

David

Permalink Reply by Chris Smith on July 22, 2012 at 11:00am

David growing plants in close proximity to tomatoes does not work well. Tomato roots are poisonous. They will stunt or outright kill other roots that come in contact with them. I have even had problems with lettuce downstream from lots of tomatoes. I have experimented with this for years and have had the same results every time. Your example is a good idea but I would not recommend doing that with tomato. Maybe try cucumbers instead. I have actually gone back to soil for tomato and water them with system water.

Using a 24 inch deep trough will be a great sump. You will have plenty of water reserve.

Permalink Reply by Josh on July 22, 2012 at 5:54pm

You all are giving me some great info and I really appreciate it.

I haven't considered the towers or nfts, but now I may have to rethink my design!

Chris, are the roots of just tomatoes or all nightshade plants poisonous? I ask because I've had issues with leafy greens that are down stream of a few pepper plants. I wonder if there's any connection.

Permalink Reply by David Stoneburg on July 22, 2012 at 6:04pm

Chris - Then I misspoke, I just remembered keeping lettuce and radishes under my taller vegies, maybe it was cukes and peppers. The AP setup I had a few years ago was zoned, lettuce on rafts, taller plants in gravel, and third was herbs, carrots, radishes and such in a pea gravel/hydroton mix. You can see that since my current garden is much smaller that I have a lot of different things on the raft; tomato starts, peppers, cabbage, herbs - and all is doing great with the exception of the occasional damping off problem.

Thank you Chris for the correction - memory isn't what it used to be. Main reason I want to get off the drugs and eat healthier!

Gotta go, picked up a beautiful Canna Lily I need to add while its still overcast.

David

Permalink Reply by Chris Smith on July 23, 2012 at 1:18am

Joshua, I am not sure about other nightshades in raft systems since I have not tried. I prefer to keep long term plants like peppers in elevated media beds to minimize my harvesting labor. I keep my short term crops in rafts where I harvest the entire raft by picking up the raft to a harvest station to do my work standing up. Once I have a cleared raft I re-plant the raft with 3 week old seedling to replace the harvested plant and drop into the trough at the opposite end.

I have a system that has had a serrano pepper plant growing for more than two years. Around that plant(now a tree) I have grown kale,chard,cilantro and now basil. The basil has grown here for more than 6 months as with the others (except cilantro) with intertwined roots. I can say that my peppers are not affecting the other plants in the media based system.

Permalink Reply by Josh on July 23, 2012 at 6:47pm

Chris,

Interesting. It's a bit hard to tell what the culprit of my leafy greens' poor production is, since the heat and humidity of the Florida Keys is not really too conducive to their growth anyway.

I do grow and clone basil all around my habanero tree and banana pepper in a media bed so I guess it's just the tomatoes that are toxic.