Media

[TCLynx]

For those people setting up new systems, there are just a few things to keep in mind when choosing media.
Primarily, you want media that won't mess with your pH too much. Things like limestone and marble will tend to keep the pH in a system very high due to their calcium carbonate, normally such medias are to be avoided. Shells might not be quite as bad but I still wouldn't recommend them as media, they keep the pH up around 7.6 which is still higher than most plants really like and causes Iron lock out requiring regular additions of Iron to the system.
There are also some medias that have a very low pH tendency, Diotamite or Maidenwell is an example of this. Using such a media will require careful observation and buffering of pH to avoid crashing the bacteria and having terrible ammonia spike.

So before you buy a truck load of the gravel, you might see about getting a small amount to run some pH tests after letting the media soak in water for a while.

FYI pea gravel usually refers to the size of the gravel, not the kind of rock, around here cheap pea gravel is likely to be limestone. Mostly quartz type river pebbles of 1/2" and smaller size are usually a fairly good choice for gravel media. Granite can also be good as can lava rock of appropriate size.
Be sure to wash your gravel before putting it in.

Perlite is generally not recommended as it can be difficult to contain and vermiculite breaks down easily. Of the manufactured hydroponic medias the expanded clay balls of high quality are the only really recommended by many Aquaponics enthusiasts.

Coco Coir, Peat, Sand, wood chips, leaves, and other such medias are generally thought to hold to much water (keep it to wet for the plants) and may also leach undesirable tannins into the water. If trying to use any of these please do it on a small scale in an experimental set up when you can easily take it offline or remove it from the system if something doesn't go right. I once tried wood chips in a small experimental set up and they turned the water so dark that I could not see the fish.

Please add more tips and tricks about media here.

[RupertofOZ]

Coco coir, peat and some wood chips can also be quite acidic... coir for example might range from pH 5.6 - 6.2....

Some wood chips, such as cypress and black walnut can be toxic... to humans, pets, and fish...

[David S.]

Do you fill up your entire grow bed with hydroton? I am going to need approximately 96 ft^3, 722 gallons, or 2718 liters of media to set up my grow beds. Their are two beds, each one with a surface area of 48 ft^2, and 1 foot deep. That would be around 1400 USD just for hydroton.

A local landscaping supply yard sells washed river gravel (1/4" to 3/8") for $28/ yd^3, which is what I am planning on using.
David

[TCLynx]

Some people fill their grow beds completely with hydroton. I never have, I've never been willing to pay that much for media when I can get a ton of river gravel for $52. Other people to get the benefit of the hydroton on the surface for easy planting but to save money and get better support for the plants from heavier gravel, will fill grow beds part way up with gravel and use hydroton only on the top surface. (Since gravel is heavier, even when it gets mixed up some, the gravel tends to work it's way back down below the surface.)

Now $28 cubic yard is a really good price as far as I know (provided they are actually providing a cubic yard, I've seen some companies figure one scoop is a cubic yard when it is really more like 1/3-1/2 a yard.) I've been buying from a company that sells by weight using scales under the truck as they fill it up.

Anyway, great price, have a look at the gravel and see if it looks like mostly quartz kind of rock or if you are gonna get stuck with lots of limestone before you buy. If it looks like rock with lots of quartz in it, definitely good choice.

[David S.]

Here is the website of the supplier I am planning on using. Now that I look at the pictures on that site, it looks like the pea gravel might have a lower % of limestone. I am in the green residential construction business, and I think that this particular company will find a way to get money from me. I am hoping to use a more personal contact with a dump truck who has much more reasonable prices, but I don't know if he will be willing to move 4 yards.

http://austinlandscapesupplies.com/gravel.html

[TCLynx]

How big is the dump truck. The place I got gravel from would deliver a load for $95 and the trucks used for those residential deliveries are not that big. Only six tons in a load tops which it takes 5 tons to make 4 yards with the stuff I got. (Made sense to me to get as much gravel in a load for the delivery fee. I've gotten 2 loads delivered since I started this addiction.)

[David S.]

My contacts dump truck holds at least 12 tons. I am not sure if Landscaping Supply has smaller trucks. The only ones I have seen are the ones they used to deliver soil to our site, which are about the same size. I bet I can get my contact to do it. I think he is hurting for work right now.

TCLynx said:

How big is the dump truck. The place I got gravel from would deliver a load for $95 and the trucks used for those residential deliveries are not that big. Only six tons in a load tops which it takes 5 tons to make 4 yards with the stuff I got. (Made sense to me to get as much gravel in a load for the delivery fee. I've gotten 2 loads delivered since I started this addiction.)

[TCLynx]

How big a system are you planning?

Just an FYI, I got two six ton deliveries of gravel. I have used pretty much all of it one way or another. My big system has aprox 1400 gallons of gravel which is the better portion of those 12 tons.

[David S.]

Right now the plan is to have a constant height in the fish tank, pump in the sump, media based system. The fish tank is a 300 gallon cube (what are those called?), and the two grow beds will be made of wood with an EPDM liner. The two grow beds will have a combined surface area of 96 ft^2, and a gravel depth of 1 ft, so the volume of gravel is 96 ft^3.

I am assuming the porosty of the gravel in my grow beds will be 32%, so I will have about 28 ft^3 of water in my grow beds (about 210 gallons).

I am planning on flooding the grow beds by using a larger pump on a timer (Laguna Maxflo 4200 - I got it for free, so I am going to try it. Max flow rate is 70 gpm, but it is only a 160 watt pump), and having a restricted drain.

I am planning on raising catfish at a final density of 0.5 lb of fish/ gallon of fish tank, but I will start with about half that, using only 1 of my grow beds.

Any thoughts? When I finish with the sketches I will probably upload them.

David

[TCLynx]

It might not take that much water to flood a grow bed filled with gravel, but for the sake of sump sizing, I always figure you need 50%of the total grow bed volume plus some % so the pump doesn't suck air and perhaps allow you to install a top up valve blow the normal low water level but above the pump burning up level.

So for example, you had 1000 gallons of grow bed, you should have at the bare minimum 500 gallons (I would personally say 550-600 is more appropriate) worth of sump tank and I would probably recommend a little more because most pumps can't pump a sump tank completely dry and the bigger the footprint, the more water will be left in it even when the pump is high and dry.

Remember that if you pump is sucking air at the end of the pump cycle when you set things up, it will only be a day or tow before you need a top up to stop things from burning up completely. Even pumps that say they will survive being run dry, will last longer if you are not doing it to them every hour.

For your 96 cubic feet of grow bed, I think I would want 350-400 gallons worth of sump tank. Remember that extra water adds stability.

[David S.]

If I actually do need that much water, then I am going to have to figure out a way to add that capacity. Right now the tank I have picked out for my sump can only hold about 300 gallons, so I might have to plumb a 55 gallon barrel to my sump in order for it to work.

Thanks for the advice! Whenever I get around to building this (the weather looks bad this weekend), I will let you know how it turned out.

David

[TCLynx]

Good Luck with it.

[Sylvia Bernstein]

I wanted to re-introduce the topic of using coconut fiber (coir), especially after hearing on the webinar last week that the team at Sweetwater Organics uses it for their aquaponic systems. I know it has a reputation for being on the lower end tolerable pH, and can contain salt if you get it from a non-reputable source. That said, there is a product out now called Cocodan Coir Croutons (http://www.composterconnection.com/site/coco-coir-croutons.html) that looks like it might work...and it is way lighter than gravel or Hydroton. Anyone working with coir? Thoughts?