Backyard Aquaponics
A place to discuss aquaponics

Im a bit confused..

I've read that the gravel should be 3/4" gravel (20mm) based on Murray Hallams dvds

?

Murray also claimed you could have 1 fish per 10L of water and many other random claims..

20mm is ok but not a necessity.

i thought 1 per 10l seemed a bit excessive!

I plan on 6 x 300L growbeds. 2x1000L FT - and was aiming for 50 fish in each tank..

That should be ok?

What would the ideal size of media be? I simply cant afford clay balls for 6 growbeds.. ($600+)

http://www.nwgs.com.au/pebbles.html is one of my local suppliers
Might have to get 20mm scoria? http://www.nwgs.com.au/scoria.html

or

http://www.gardenandbuildingsupplies.co ... -toppings/

We recomend 25 fish per 500L of filtration, assuming you will grow them out to around 500g. But there is many other factors to take into account. With new system 'un-cycled' it is safer to stock lower and then build up to your 25 per 500L. I like fishless cycling until a solid nitrate colony is developed.

Another thing to consider is 50 fish in a 1000L IBC @ 300-500g is really crowding it and there growth rate will reflect this, they will be stumped with fat stomach's. Dont forget they need room to swim.

Personally Id only have about 35 odd fish in each FT.

In relation to media, the options are endless. Blue metal and pea gravel are cheap options here in Oz.

That's your problem right there !

I did find the dvd i brought quite dissapointing............
From here on its google and forums alllllllllll the way.

1/2 to 3/4" gravel is where im leaning - red scoria or blue metal..
Im currently trying to plan my sys correctly (see url in my signature for sys plans)

I think i'll use a 90mm SLO and 90MM primary pipe to the 3 growbeds on each side, then run some 40mm tapped outlets from this into the GB. then dump into 2 sumps - pump into FTs via spraybars..

should work............. i hope.

Hi al, has anyone tried using a large grain sand?

We have always used the expanded clay that's 8-16mm and that's 0.31 to 0.63 of an inch.

sand would eventually clog, would have poor oxygen retention and also flush through your media guard into you FT etc

I know of some one who did some testing with sand. It required pre-filtering to keep the solids out of the sand bed and all sorts of extra to keep the sand from washing out of the bed so I wouldn't recommend it for standard operation.

I've used mostly 1/2" river gravel (10-15 mm I guess) and been fine with that. More lately I'm testing out some of the expanded shale/slate products but still the 1/2" range. I'd like to try 3/4" too but it is harder to come by.

I think if you rinse your media and stock your systems appropriately for your filtration then 1/2" media is just fine.

I will admit that so far my media observations have been that my smaller pea gravel media (10-15mm) is working better than my larger blue metal media (20-30mm). Its been said that smaller media will clog over time but I think if you have a good worm colony this wont be an issue.

Sand makes an excellent fine particles filter media, but those properties make it unsuitable for GB media. The way I think about this is, you want a media which filter solids from water, but on the contrary is not an excellent filter of solids from water. Gravel, beads, clay balls, etc all make great GB media but would be of limited use in a fine-filter; sand, scouters, Brillo pads etc make good fine-filter media but you wouldn't want them in a GB for those same reasons they make excellent filters!?

And then, there's compaction which rules out other medias such as nylon and plastic floss, etc.

It will also depend on how you are filtering or using the word filter.

You can settle out solids in a large empty tank if the water flow is slow enough, that is a sort of filtering without any filter media even. While a sand filter tends to be under more pressure and the water is being pushed through rather harder to the sand needs to catch more of the particles even with the higher flow/pressure through the space. Our media beds are between these two extremes. I expect that most solids captured by our media beds are tending to settle out of the water into the gravel or grow bed media more than it's being "filtered" out of the water. And as a grow bed builds up it's nice coating of bio-slime it will become even better at catching fine particles. But Like with a settling tank, if you do something to stir it up, solids will get through it until things settle back down.

I know its not very cheap but what about crush coral as media?