Hydroponics in big water tank?

Hi,
As a total beginner, I am thinking of setting up a diy hydroponic system in our greenhouse.
In the winter I keep fish in a large water tank (a horse watering tank, approx 1500 liters, 1.8m x 1.2m x 70 cm deep) I am thinking that if I make a lid for this and cut holes, I could use it for hydroponics in the summer.
I already have a water pump (max 200l / hour), and a good air pump. The water pump I hope to use to circulate and also to pump up for a drip system. All the systems I see are in much smaller buckets for deep water hydroponics.
Is there anything against using a single tank this size for hydroponics?

 

Worth looking at Aeroponics (basically the nutrient is sprayed onto the roots, which "dangle" above the tank, but do not therefore stagnate. If it doesn't bother you to do so its well worth reading the forums (not this one!) about illicit drug growing using Aeroponics - there is a wealth of information, which obviously translates to other crops, and they have become very successful got it down to a fine art.

You could also consideraquaponics which would combine your fish and hydroponics. I don't know anything about that though.

Personally, I think deep bed hydroponics is the wrong approach - the roots need air. My personal expeerience is with NFT (Nutrietn film technique) where a small amount of nutrient trickles down a trough in which a mat of roots grows (and capillary action draws it up amongst the roots), and the house plants use in office landscaping which sit in expanded pumice type granules (I don' thitnk you will get crops from the latter, but I could be wrong).

I have grown Tomatos etc. commercially in NFT - a long time ago though!

 

I`ve grown chilli`s using aquaponics.
Rainbow trout would do well in the winter if you can keep the oxygen levels high enough.
Flood and drain using gravel filled growbeds is the easiest way to do it :wink:
I think you`ll be in for all kinds of humidity and condensation problems with the tank in the greenhouse though.

 

"Flood and drain"

I'd forgotten about that. Good idea.

 

The most common method with aquaponics is flood and drain gravel beds with either auto syphons or the pump on a timer plus a slow drain. The solids build up in the bed (its like brown blancmange hehe) so you add a few worms which soon become hundreds and the plants can have all the goodies.
With DWC or NFT aquaponics, you have to filter out most of the solids which contain most of the P,K nutrients making it harder to grow toms or chilli`s,its ok if you want basil or lettuce though.

For normal hydroponics, a 1500L nutrient tank would be pretty expensive on hydroponic nutrients..i guess you may need to add at least 4L to get a reasonable EC reading :wink:

Aeroponics, in its true form uses high pressure (min 60psi) in very short bursts of just a second or two. There are plenty of products that sport the aeroponic label but most deliver anything from a spray to a sprinkle...not exactly a 50 micron mist :wink:

Its good to try everything at least once.

 

Thanks for the info and ideas. Aeroponics will have to wait for now. Landed on a flood and drain idea. 500L water in the tank. Old plastic table on bricks half way up. Covered in a pond liner, to make a top tank. Hole in the liner to drain back. Water and air pumps under. Fertilized (not sure it was the right type), and some nice bacteria, at least the fish like it. Air pump going all the time. Water takes 30 minutes to fill the top. Filled the pots and some of the top with, with Perlite.

It’s off with a load of tomatoes. Soon know it it works.

Thanks all.

 

As long as the pump can outrun the hole in the liner you should be ok, you`ll need a timer too. Bear in mind that perlite tends to escape and can end up everywhere :wink:
Here`s how i had my above tank growbed arranged, it used hydroton to cut down on weight.. gravel is much cheaper.
The pump runs 24/7 filling the bed until the water level is 40mm below the hydroton. The auto-syphon kicks in and quickly drains the bed back to the tank(fill - drain time ratio is usually 2:1)
As the growbed empties it breaks the syphon and begins the fill cycle again. Note the feedpipe runs through the overflow pipe on the right so theres no chance of a flood :wink:

edit: if you are going the aquaponic route you`ll need to cycle the system, the best way is to use pee instead of risking the fish.
Google for "fishless cycling".

 

Nice diagram

 

cheers Kristen
Its the safest layout for indoor use,theres no chance of ending up knee deep in water :wink:

 

Is there a ballcock, or somesuch, somewhere so it replenishes? Although I suppose the reservoir will last a long time, i.e. to cover transpiration / evaporation, and topping up only needs to be occasional??

 

The "reservoir" was a 140L aquarium with fish in it :wink:
The trick is to flood the bed to 40mm below the top of the hydroton/gravel which minimises the evaporation.

 

"The trick is to flood the bed to 40mm below the top of the hydroton/gravel which minimises the evaporation"

Ah, I see. Got it.

Not sure I can get galvanised into action to try it though - too many projects on. I'm trying to be more organic anyway ... but it might feed the world when the population has grown so that we only have 1 sq.m. each and live in tower blocks several miles high ... :(

 

Imagine pulling a few lettuce and other salad stuff from the growbed and then netting a couple of fresh rainbow trout from the tank to go with it :wink:

 

Hi Hex,

I still don’t know what I’m actually doing! It looks a bit “Flood and Drain”, but I’m not using the fish in this, so I add liquid fertilizer to the reservoir. When I now look at the cost of liquid fertilizer and that it’s applied weekly and I have 500L, this don’t look too cheap! So… my thought is, can I just go out to the garden pond filter and collect “liquid fertilizer” from the sump? Is that “liquid fertilizer” or is it just waste? I have about 10 KG of fish out there, so they must produce something.

Perlite was a bit of a rash choice. The whole thing floats! It’s staying in the tank at least, and packing in pots just about stops them falling over.
I’ll probably add a bit of gravel to give the roots something to hold onto. Your auto-syphon looks perfect. My cut in the liner is working fine, but it probably trebles my filling time, as it empties while filling. It may also either clog or enlarge in time, so your auto-syphon will be going in. At the moment filling takes 30mins and empty takes 10mins.

 

Hi Fishfish,
Any chance of some pics showing the layout to make it easier to visualise?
You don`t have to have the bed over the tank, there are a multitude of ways to do it. Gravel beds are the cheapest option, they anchor the roots too..unlike perlite :wink:
The water/gravel ratio can vary from 1:1 to 1:2, the fish weight is geared to the gravel which is the biggest factor for the bacteria.
The hydroponic nutrients generally have all the elements, the pond water will probably be missing some so you may have to supplement to get healthy growth depnding on what your growing.
If you can get the water and the solids periodically running through a gravel bed with a healthy worm population in it you wont miss many. Iron is about the only thing that needs to be added from time to time.