Backyard Aquaponics
A place to discuss aquaponics

Definitely will be going all male tilapia. I'm going to start out at about 1/3 the recommended load for this system and see just how far my nutrients will go. I'm hoping to be able to see on my DWC beds where the nutrient levels start to drop

Oh, and as for your mystery fish in your system, I didn't see a great picture (was interrupted reading), but the ones I saw made me think they were possibly mosquito fish... Gambusia. They are a live bearer very similar to guppies. Some killifish are also live bearers, but many of them are egg layers, notably some that can lay eggs in areas that completely dry out, then reconstitute and hatch when the rains some.

Yes I did finally identify those little fish. Least killfish or Dwarf livebearers. They got into the system with the duckweed and as I was netting tilapia fry out of the duckweed tank, they wound up in the aquarium with the fry.

Ok, so when you get to the point of starting your system thread, I'll be interested to hear the details of what solids filtering and bio-filtering and all you decide to put in. I know there are others out there interested too.

As you cycle up and stabilize the system, going light on the stocking will be a good choice. Once things are going well (say during the second season or batch of fish) that would be the time to start increasing stocking to see where the limits are.

What do the laws where you are say about keeping tilapia?

I am good to go as far as keeping tilapia in Arkansas. They've even put them in some lakes, knowing they won't make it through the winter. They can get some incredible growth out there in just one season. At least one of the Universities in Arkansas is working with aquaponics and tilapia, and I think there is a commercial fishfarm that produces tilapia fry.

Temps in the winter and heating the system are my biggeset concerns about year-round production. Most of what I've read about catfish and tilipia seem to indicate that the preferred temps for them are not exactly compatible, but fall into a less productive, "tolerable" range. TC, what is your system water temp? I was curious if the skin problems your cats were having was from the temps being on the warm side for them.

I may run my system all winter without any fish if I do this in the garage, just to see what I'm going to have to do to keep it the temp I want. I have my doubts that when it's 30degrees F outside (about -1 C) and colder, that I'm going to be able to maintain an adequate FT temp. I was planning on enclosing the area with heavy plastic sheeting, and likely do some space heating inside that enclosed area, but that would restrict my airflow. I considered running a flexible duct from the house to that area as well, but I think the distance it would have to travel would be too great.

Why, oh why can it not be 74 F all the time?

Actually, optimum temps for the catfish is around 80-86 F and I would probably count that as optimum for the tilapia as well. Both will survive up to 90 F.

Actually the skin issues I had most recently with the catfish was in the spring when water temps were still low.

Fish have been fine over the summer except when the three really big catfish started fighting a while back. Now there is only one really big guy as we ate the other two.

With DWC you will probably have an easier time keeping temps up than if you were doing flood and drain gravel but you will still have a challenge heating over the winter. Heck, I had a problem during a cool week with two freeze warning nights here in FL and I was only attempting to keep the tilapia alive, not growing.

If doing plastic film for the greenhouse, you will probably want to do double layer and inflate in between.

Seeing as how 82-86 degrees F is the optimum temp for tilapia grow out, I'm wondering if a tankless type water heater would be able to keep up with keeping the tank at 86 degrees(the minimum setting for the heater). These heaters are designed to be used "by demand" though, so continuous use of one might cause a problem, and they aren't cheap. Is there a formula to figure out heat loss from a body of water based on the ambient temp and humidity?

And you would want one with a temp sensor in the inlet since most of them are designed to work with a constant low incoming water temp and they heat it some constant amount to get the desired water temp. If your inflowing water is already warm enough and you heat it more, that might not be so good. (you would probably want to look into one that is designed to work with solar water heating.)

However, if you can come up with some sort of thermostat controlled pump that would only turn on to pass water through the heater when the water dropped below a certain point, then perhaps such a heater would work.

Beware of copper pipes though as copper in an ap system might not be such a good thing.

Hmm... the copper thing I hadn't thought about. Heh, would make my incidence of ich low... right up until it killed all the fishes. I imagine the guts of those things are copper, but I guess I could investigate them. As for the temp monitor, the majority of them have an incoming temperature gauge and an outgoing threshold, and they restrict the flow internally to reach that target temp, so they are very smart. Any way I go with tilapia around here, I'm going to need to do some major heating in the winter. Not sure its worth it, but I sure had my heart set on tilapia. I've been taking a second look at hybrid bluegill, just because I know I can provide adequate temps for them, being a native species. Their growout period is at least twice as long as tilapia though, and they're a 90% male population, so I'd still have to either sex females out, or make sure the tank bottom isn't usable to breed, or cage them.

Thanks for being my sounding board TC.

Rupe has been doing experiments with evacuated solar tubes for solar heating his water. I've got a couple pool heater panels on my roof that I had a heat exchange thing set up to run at night to warm up the fish.

You might look into koi pond heating systems.

The koi pond heater looks promising. Temps here average from 30F to 93F, with records of -8F to 110F. So planning on 20F or so as a low would most likely get me by, as it will be inside and I would insulate it as well. For times that cold I'd probably make a top as well.

I've been having big problems finding what I feel is an acceptable fishtank. I've been thinking about making one. Not only would it help on arranging everything in the space I have, but I could customize the water flow through it, to aid in the removal of solids. Instead of a round tank that I "try" to get a circular current in, I could have a rectangular "run" tank and try to move all the solids to one end where they can be evacuated.

As for tilapia and stress, have you lost any due to what you thought were stress related issues from handling, and if so what exactly happened with them?

When I got my first batch of small tilapia, a couple of the little ones did die of something or other within the first week or so and not that big of a surprise when getting 100 or so new fish.

As to stress from my handling, I don't think I have had any deaths directly from that. However stress due to fish domestic violence has killed a few of my attempted breeder fish when I was trying in a small tank. I lost a couple smaller fish to swimming through pipes or no holes overflows onto the gravel. And I lost one larger tilapia that managed to jump out of a bin I was using as a tank. Tricky part was he had to hit the lid hard enough to pop it open and then jump again to actually get out. Breeding or the males trying to chase the females tends to result in lots of jumping and splashing especially in smaller tanks.

Tilapia are really quite tough fish. I would avoid handling them much or stressing them when the temperature is down though.

Tilapia are also pretty happy with fairly high salt levels so you probably won't be growing lots of strawberries if you keep the salt up for the tilapia. Then again, my tilapia seem to be doing fine and I haven't added salt to my system for ages and when I dipped the EC meter in today, the reading was barley above 0.

I have seen tilapia decide to jump out of buckets when they decided they don't like the water anymore. This was when I was clearing all the fish out of the duckweed tank (I think there was quite a bit of undesirable dissolved gas build up in the water and a dozen little fish in a couple gallons of the water shortly had them jumping out. I saw it happen and collected them back up since they were destined to be chicken snacks anyway.)

Hmmm, after a lot of thinking I'm considering becoming a GB follower. My main reason for the DWC beds was so I could "see" my nutrient levels in the beds. So I could tell when I didn't have enough, as evidenced by slow plant growth towards the ends of the beds. I was also looking forward to NOT buying media, cause I'm tight like that. Still, I can do GBs and put in some NFTs after (would need a flow solution) and be able to see nutrient drop perhaps.... Plus I wouldn't have to deal with solids removal.

I wonder what magnitude of aeration would be required to digest solids as opposed to separating them in regards to running DWC....

I don't mind being "hands on" with solids removal. I don't need an automatic solution. Heck, I had planned on vacuuming the bottom of the FT daily provided the fish wouldn't mind.

Because the system is a closed loop... with continual nutrient inputs... and extraction....

Any "signs" of nutrient deficiency will be seen across all components and plants (generally - some plants have lower needs).... can't speak from personal experience of DWC.... but from those that have... and hydro experience.... the postition of the plants generally doesn't reflect any nutrient loss...

Unless, in the case of hydro... you have a section of mature very heavy feeders followed by a section of new plants... and even then I think it's more a case of flow rather than nutrient variation....

Remember the nutrients are in solution... distributed evenly.... as long as the solution gets to the plants, at any postition... the nutrient solution/concentration is the same...

What I've read on other sites, particularly about NFT hydro it states you must limit your run lenghts or suffer depleted nutrient level by the time the solution has reached the end. Since the flow through a DWC bed is also linear I wondered if you could see that same effect over the length of your tables. Granted there is more water in a DWC and it's being agitated by aeration, but you have to admit since there is and entry point of nutrient rich solution that the outflow will be at least somewhat depleted based on your plants' demands.

Nope.... in hydro this may be the case if lengths were huge.... (most tables are 6m in length)... and the nutrient solution wasn't monitored closely....

OR... if the flow rate at entry and exit point differed markedly.... and that's more the reason for limiting your table length than nutrient depletion...


As I said ... in aquaponics, because we're constanly feeding the fish, and the fish are constantly respiring... we are continually "topping up" the nutrient load... and continually circulating the nutrient load...

Ignore your nutrient concentration, or water temp & pH in hydro... and yes you can end up with deficiencies... generally across all plants within the table... unless mixed, and/or at differing stages of growth...

My point was that, just like in NFTs that have been overextended based on their nutrient level, I was curious if you could see nutrient depletion in a DWC if your system was that close to the "balanced" point.

Even though you stated that:

RupertofOZ wrote:
Remember the nutrients are in solution... distributed evenly.... as long as the solution gets to the plants, at any postition... the nutrient solution/concentration is the same...

That's only roughly true with single pass GBs is it not? It's not true of your NFT runs, and it's not true of the water coming out of any bed. If that was the case then we'd never have to add anything to the system...nutes or food or anything. The plants take some nutrient from the water. The water leaving a bed, particularly a NFT or DWC bed is going to show depleted nutrients. You could say it's true of "useable" nutrients if your nute levels are way above what could be pulled out in one pass anyway.

Regardless, it's not a point I wish to argue. It was merely me wondering if you could see it happening in a DWC bed as opposed to a NFT run.