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Dirt Dobber
09-13-2009, 09:07 PM
Hello all, I will apologize in advance if I'm stepping on someones toes (as I have in the past) I'm confused about rafting. If the bacteria on the gravel change the ammonia to nitrates that the plants like -- How are the plants living on the ammonia water they are floating in? :?

jackalope
09-14-2009, 07:20 AM
I think you'd want to run the water through a sump first and then into a rafting pond, if it's Tilapia you're raising, becuz they'll eat the roots off, and that wouldn't work so well ;).
You also have to remember that in the wild, the plants do their thing just by floating on the water (Duckweed, water lettuce, etc.) and the bacteria that do the work are in the sand and detritus at the bottom of the lake, stream, etc. so the plants will still grow, and the fish will survive because nature does what it's supposed to.
In the raft system you're probably asking about, if you've put some gravel on the bottom, with fish and then rafts on the top, you've still got the place for the bacteria to work ;) I'd still use a sump though anyways, because it's a closed system and the sump (IMHO) would do a better job of removing/converting the ammonia and nitrites. Just my outlook on the question as I see it .... others may have a different point of view.

BTW, asking questions is what the forum is for, so you're not stepping on anyone's toes here ..... Welcome to the DIY Aquaponics forum!! Glad to have you here ;)

Dirt Dobber
09-15-2009, 01:34 PM
:geek: Thank you for your response. It is as I suspected. I figured it would have to circulate through a rock bed of some sort. I'm using catfish right now so the roots will be fine. I can't find Talopia fingerlings anywhere here (NC/USA) :(

jackalope
09-15-2009, 06:52 PM
There are lots of availabilities for tilapia ........ check out the classifieds ....... ;)

Oliver
09-15-2010, 06:09 PM
"If the bacteria on the gravel change the ammonia to nitrates that the plants like -- How are the plants living on the ammonia water they are floating in? "

The ammonia is converted by the bacteria that is found in the bio-filter, be it a separate unit or a media filled grow bed.

It is important to remember that recirculated aquaculture systems, including aquaponics, are multi-pass. Each time the ammoniated water is passed through the bio-filter, some of the ammonia is converted to nitrites then nitrates. Not all of the ammonia is converted on each pass through but by continually recirculating the water through the system (fish tank, bio-filter/grow bed...) then the process continues as well. The more ammonia then the more bacteria populate the system so it is self regulating.

The ammonia is being added to the water by the fish on an irregular basis and the bacteria are constantly doing there thing of conversion. If everything is in balance then the ammonia levels will be low and the nitrate levels will continue to increase.

Enter the plants: The plants in the system, regardless of their location (as long as they are part of this multi-pass recirculation system) up-take water, nitrates and minerals.

So, there should be very little un-converted ammonia in the system, levels well below what the plants can tolerate.

It all comes down to this: the more you feed your fish, the more nitrates you will have in your system. The more nitrate sucking plants you have in the system, the fewer nitrates you will have. This balance is up to you, the farmer, to keep a close eye on. Monitor the water quality regularly. If you find that you have an ammonia spike, then stop feeding your fish until it settles back down to normal levels. Again, monitor your water quality regularly.

The above explanation is for a fully cycled system that is at least several weeks old.

I might add that it is important to aerate your water in as many places as is practical, for the bacteria need oxygen to do the conversion, plants need some oxygen to grow and fish need oxygenated water to live. Don't ever turn off your aeration system. The best aerators I have found to date are AquaFuse lines that put out fine bubbles. After replacing my air stones with these diffusers my dissolved oxygen went up over a whole point.

It is also best to leave on your recirculation pumps as well. Attempting to save electricity by turning any part of your system for a period of time can, and most likely will, kill fish.

Some other unsolicited advice: Stay away from DC pumps, as I don't know of anyone who has not had them fail in time. Stay away from any kind of start/stop switched water pump for this shortens the life of the pump's motor and adds another failure point via the switch. Use siphons to time your flood and drain if you go that route.

Oliver

Brier
09-15-2010, 07:28 PM
The post above mine, is good stuff! My impression is that if you are using a raft system, you really need a good biofilter to take up the slack that growbeds usually take up. You will need decent surface area for bacteria to colonize on. Your raft will not provide it alone. What it will achieve is the uptake of nitrates, and reduce the need for water changes. You would be best to structure this as a recirculating aquaculture system, with the added benefit of plants utilizing your final by product.
If you are looking for tilapia, there are several guys here that would probably help you out. Badflash has Mozambiques, not sure if he ships, but am sure he can steer you in the right direction. I have blues, and if you are interested in blues, I could help you out as well. Either work well, I think mozzies are easier to breed, and blues grow a bit better. Good luck with your set up!