Backyard Aquaponics
A place to discuss aquaponics

I'm sure it is (in fact I think I've seen it) but I did a few combo searches after coming up with over 600 references to sand and didn't get lucky. I thought that I could spend an hour looking through these or I'll just wait until tomorrow and measure it then. Which is probably better any way because every medium is likely to have a different void due to the different range of particle sizes and shapes.

My sand arrived

Its a mix of large grains down to small and while I think it is going to be good for my first layer of lime render I don't think it will work well in a growbed that is going to be flooded. Main reason for this is that when tresing to check its void I had to wait for the water to sink in before tipping on the next litre.

Any way the void was 30%.

Using the example I used on page 2 of this thread that means:

V1 = Volume of water in the top 27.5 cm of FT.

V2 = Volume of water required to fill Tidal GB to a depth of 27.5cm.

V3 = V1 + V2 = volume of water required to empty FT and Tidal Growbed
= Volume of water required to fill f&d GB

G = Void % in gravel to be filled with water (45% in the gravel I've measured)

A = Area of f&d GB that is filled to a depth 27.5cm and is required to balance system.
= V3/.275/G

V1 = .275 x L x W = .275 x 1m x 1m = 275L

V2 = .275 x L x W x G = .275 x 1m x 1m x .3 = 82.5L

V3 = 82.5 + 275 = 357.5L

A = 357.5 / 275 / .45
= 2.9m2

So a 1m x 1m tidal bed full of sand would need to be balanced by a 1 x 3m bed full of blue metal.

That compares to a 1m x 1m tidal bed full of blue metal would need to be balanced by a 1 x 3.6m bed full of blue metal.

Probably be a good idea to have the f&d grow beds a bit bigger because there will be a little extra volume in pipes and such and if the f&d GB isn't big enough then the tidal GB won't fully drain.

Thanks for that SC, others who have voided gravel have come up with similar figures (ranging between 42-45%) - so using 50% makes mental maths simple maths and adds a small fudge factor

One issue popping its head up so often is the wastes building up at the bottom of tanks. I just wanted to comment on a a couple of things:

1. Some peoples pumps have been getting clogged up in the tanks. Ive been talking to a local gardening shop owner who also seems to think that its partially due to pumps on the bottom of tanks.

2. Obviously its because they are drawing in water, and so solids will be attracted to them etc

3. Water needs to be pumped from the bottom of the tank to the top of the tank so solids are spread around and not gatthered at one place like the bottom

4. Trial suspending pumps 1/2 way down the tank. In this way they might not get so badly blocked.

Id be interested to see if anyones tried this or has answers themselves. Aquamad has ect.

is best not to put the pump on bottom of the tank because if any thing goes wrong it cant pump out all the water.

I had mine near the bottom and it did well tking the solids out. As a precaution to what CG said, I raised it about halfway in the tank and it works well, clogs less but there are definitely more solids on the bottom of the tank.

This is the trade off you make with pump selection.. It is best to get as many solids as possible out of the fish tank, so avoiding pumping solids because the pump is getting blocked, means that the pump isn't so well suited to the purpose.. This is part of the reason I love my Ebara pumps, sucking up 10mm solids is just beautiful. It's also part of the reason why I tend towards larger pumps running for shorter periods of time... Yes, small pumps running for longer periods are great but they can't deal with solids and something has to deal with the solids..

Of course another way is to use the method of pump in drain tank, like MF, VB, and my newest system uses, then your pump isn't in the fish tank at all, so it doesn't clog as easily..

Totally agree EB and this is the way I am heading as soon as my 2,000l tank is ready...the sump tank (with smaller pump) is okay with fingerling sized poop but 500g fish and 3,000lph pumps may not mix that well

Joel

A flow form as a return may work well from your floating ratft tank all although I dont know how much they airate the water.

http://www.flowformsamerica.com/

I still haven't worked out where to fit one in my systems yet Matt, GD had a flow form, I don;t know if he has put it into one of his systems yet.

Hi Joel ..

Maybe I can pop around for a beer one weekend soon ( I will bring the tinnys ) and see if I can describe what I have in my head regards a "tidal" system.

Then maybe hopefuly you can point me in the right direction regard my plans for aquaponics at school!

Hi,



I have a 4500 lph pump (on the bottom of the tank), 500g fish and a clean tank bottom.....and I haven't experienced clogging problems yet. The reason my system has remained trouble free (so far) is that I periodically (usually every couple of weeks) blow through the pipework to remove any build up of solids and I have 44 larger fish in 600 litres of water so things get stirred up fairly well.

Fish poop (and uneaten food) on the bottom of the tank generates ammonia. This more likely to be an issue in a small system like mine than one that is 3,000 litres or more.

I do have a set of flowforms.....and they do aerate water very well.

They are too big for my current system but I'm planning to incorporate them into a future larger unit......or possibly as part of my proposed grey-water treatment system.

Gary

Hey can some one tell me what a flowform does?
What benefit of using a flowform in aquaponics? [highlight=red]would a bunch of bottle caps placed in a nft pipe constitute as a flowfrom?[/highlight]

All I can think of is that it might improve aeration and or be decorative. The bottle caps in a pipe might technically be a flowform, but I wouldn't consider it decorative.

Hi,

The bottle caps in an NFT pipe might serve to aerate the water but they certainly wouldn't be a flowform.

Flow forms use a figure of 8 movement to stir the water.....aerating and reinvigorating it. They are supposed to emulate the natural movement of water in a swiftly flowing stream.

The action that they produce has the effect of lowering the Biological Oxygen Demand (read pollution) of a body of water.

For more information and lots of pictures.....

http://www.nationalwatercenter.org/flowforms.htm

Gary