Backyard Aquaponics
A place to discuss aquaponics

Hi again!
I've a question about the use of coral debris (sand) for either hydro- or AP.
It happens that I may be involved in a project at some atoll where (what seemed to be sand to me) actually was sediments of the surrounding reefs.

The question of 1000 points is here if this stuff (after being sieved down to the right caliber) is suitable as medium. I can figure out that it has a high calcium content, and that it has to be cleaned well from any organic or saline residues. But that's pretty much it. The question probably turns around its chemical stability, when mixed up with fish waste or hydroponic nutrients.

Straight from the gut, I'd say it would be suited and chemically stable - but any more intel, ideas or objections would greatly help and be appreciated!

Thanks a million!

Cheers,
Lucas

I'd suspect that it would be too fine for any flood & drain application in aquaponics...

Might be alright as a seed starter medium in hydro...

And would probably be worth either mixing some in a growbed... or under the water return .... as a "buffer" ... ala... shellgrit...

I am/was aware of the "too fine" part of the deal - that's why I was going to sieve only the bigger caliber out. Actually, in quartz based river sand one cannot detect the bigger caliber parts that are hidden (up to pea size). But than again I haven't seen or touched the coral stuff for real yet! What about debris or sand around Barrier Reef? How rough or how fine is the stuff around there - and may I be right with the fact that there may be different calibers. If yes, it may take some time and labor but it will be suitable - will it?

Because the point here is that there is nothing else suitable around except that stuff and any gravel or clay pellets have to be shipped in - and that's very expensive. The location is kinda remote!

Thanks!

I take your point about location... and cost Lucas...

But generally I wouldn't recommend a media less than 10-15mm .... minimum...

Also... due to its high calcium carbonate composition... filling your growbed with it... will play havoc with your pH.... probably dragging you perpertually to about 8.0...

Given your heat, and possible evaporation issues... maybe a mix (haven't tried it myself), of coconut husk fibres (acidic)... and some coral (alkaline) might work for a pH balance...

And aid water retention in your environment... you might just have to experiment with the right mix... and flood times... so that the coir doesn't stay too wet...

I expect that coral is gonna be somewhat similar to shells as media, it will (at least for the first year) cause a pH that will be higher than optimal. If you don't mind supplementing Iron and skip trying to grow acid/iron loving plants then it might be ok but understand the limitations. I took one for the team and have about 40% of my media is shells that buffer to 7.6. It has taken a year and a half for one system to come down in pH to something close to 7 and the big system is still hanging around 7.2-7.4 and another system is a solid 7.6 to 8 still.

Yes it can be done and if there are no other choices, for media, then you will have to deal but a high pH is gonna be the cost.

It might be worth you looking into other growing methods than flood and drain gravel for the majority of your filtration and only have one bed of flood and drain coral to act as your pH buffer and grow larger plants then perhaps you could use the DWC type methods with separate filtration for the balance of your system. These are just some options to look into.
I personally like flood and drain gravel beds for low maint systems but if it means struggling with too high pH then it might not be worth it.

That doesn't sound very good, actually...
Mainly because this project is in fact not supposed to have (that) much room for experimentation.
This is also due to the fact that it is indeed very remote - and furthermore we deal with a high end enterprise in the foreground. Expectations are very high, everything there is expensive and there will be no room or tolerance for any "playground" - no way (unfortunately). I guess I have no choice and must opt for playing safe if I get involved for good. And that probably means hydro and no aqua as well.

PS: As for the coco husk fiber I have been experimenting with shredded husk for a while in Hydro. It is fine for some plants but not for all.

1. It tends to keep a permanent high moisture, which some plants tolerate, others do not.
2. It decomposes over time and transforms to some sort of swampy compost.
3. It doesn't actually lower or buffer the PH (in a lower range) very much. At least not from my experience and collected data. But here I am talking hydro and a range between 6 ad 6.5.

Thanks anyway guys!
Cheers,
Lucas

Yep you're right about the coco coir... only way it can work is in a very slow drip feed.... or more particularly, an intermittantly watered situation... with a drying time between watering cycles...

Well, because of this, - I came to make my own "semi-organic" substrate mix for my hydro.
It contains around 10-15% shredded coco coir (or husk), some 40% hand sieved rough sand, about half of it is rice hulls, that I get for FREE from a nearby mill -plus some pea sized gravel on top. And either basalt debris (concrete size = 6-15mm) at the bottom of each pot or bucket for good drain - or alternatively a hand full of my shredded coco coir at the bottom for keeping moisture.

Both, the finer coco coir and roughly shredded version ALONE are very fine for drip and waste (which is mostly evaporation anyway) as well. Not very ecological so far- but D&W is anyway not done in AP, I guess...

What I am using looks a bit like this stuff, perhaps even rougher. I get it very cheep or the whole coir for free - but need to shred it myself with a machete then.
http://www.hydromall.com/UserFiles/Imag ... oir_lg.jpg

Just to make sure that it's actually not me who aims for high end - but the project I was talking about definitely is five and a half stars, through and through!

Don't know if you can get it over there... but here we can get coir "chunks"... 20-30mm... which allows a bit more air into the mix...

Yeah, that's what I've got (and meant by rougher as shown at the pic). If I shop/shred it myself from whole coir chunks, I can anyway cut it down to any size I want, from half to quarter coir to finely 'minced'.
I still have the option with coco coir with that project, depending on availability (most likely) of coir at the atoll. But then again, I guess there is even no understanding or time for shredding it on cite I guess. I can't abuse of the 2 world class top chefs either, to have fun with that job in their free time...

Otherwise I'll probably go for "camouflaged" DWC. Which means a reliable but rather low tech deep water heart "hidden" underneath some sort of tropical garden 'ambiente'. Not sure if you get what I mean by this... but that's anyway another story to be worked out in 3D simulation