Hi Deon - your post here states that you have 50 tilapia but the profile page states 15? A great many things could potentially be an issue in a new system, and with very little to go on in your post regarding the age / design of the unit, I would like to suggest you go through (If you have and ruled them out I'm sorry to repeat) the following checklist of possibilities:
1) Is the system scaled to operate effeciently? Are you adding enough nutrients to the system to keep your plants happy? The rules of thumb section on the home page should give you some idea. In a system that is not scaled correctly, you could have all the parameters looking right but unhappy plants because there is not enough nutrients to go around.
2) Is the system recently cycled? You supply no data on water quality and nutrients. You should have a pH of between 6.8 and 7.5, and no serious ammonia or nitrite readings? If you still have high ammonia or nitrite readings, your system could not be cycled fully. Please note that aquaponic units do take a few weeks to kick in properly and you could expect a slowish start with gradual improvement as time passes. If you plant high nutrient demand plants in a young system you could have potential problems.
3) Can you diagnose a trace element shortage in your plants from your hydro background? It sounds like it from the description you gave, but as I'm colourblind, I do not know these things as well as I should. In younger systems, you could potentially see some iron, manganese, potassium or molybdenum shortages as fish food is composed slightly differently to plant nutrients withe respect to those trace elements.
4) What is the nutrient component ratios of the fish food? Your AP system will only be able to supply what the fish food contains unless you supplement. I always recommend going for the best food you can afford, as these are typically better formulated - the guys on the forum can advise on the food of choice in the US for tilapia.
5) In the response, I am excluding light as a potential issue, as you did not mention it as a concern.
I hope the shortlist points you in the correct direction for problem solving here.
Regards and welcome
Yes as Kobus says, you haven't really given us much info to help you with.
New systems it is kinda common to dose with some Maxicrop or other seaweed extract to help with the trace elements and potassium.
Tall spindly lettuce though tends to make me think lack of light or the light is too far away. When I was trying to grow lettuce on a shady patio I was getting 30 inch tall plants with leaves like every 5 inches. Lettuce may be able to grow under lower light conditions than most plants but it will also stretch for the light and not grow bushy heads if it's too shady.
But back to the suggestions above.
Check your system water tests and let us know (if you don't know anything about water testing check this link)
Also water temp
And how much grow bed space and what type of grow bed and filtration you have to support those fish? I kinda like having a cubic foot of grow bed (7.5 gallons) per fish for a new system.
As to the fish food. Most pet store fish foods are formulated to keep fish healthy while polluting the water as minimally as possible since the more nutrients the fish food provides the more the owners will have to clean and change water in their aquarium. Now in Aquaponics we want those nutrients for our plants so you might be better off looking for a fish food with higher protein that is designed to grow out fish more than keep the water changes down.
There are several other types of good commercial fish food out there but I'll tell you how I get the food I use (it's not perfect but it seems to provide good results till something better is developed.) Anyway, I use Aquamax 4000 for most of my fish feeding. It is a Purina Mills product designed for omnivorus fish like Tilapia, Catfish or bluegill growing in a recirculating aquaculture system (it provides all the dietary requirements to grow the fish out in a tank.) It also seems to do a good job providing for most of the nutrient requirements of the plants once the system matures. So, I went to the Purina mills web site (you can find it by searching Aquamax) and I entered my zip code to find a dealer near me. Then I call up some of those feed stores and find out if they are willing to have a bag of my chosen feed put on the next purina delivery truck and how much they will charge me. Helps to find out their ordering and truck delivery schedule too. Feed store I go to usually orders Monday Morning for a Thursday delivery. You don't really want them to keep fish food in stock unless it is selling regularly since fish food goes bad quickly. It comes in 50lb bags and might cost anywhere between $24-$38 (for the 4000 dense culture feed) this way I expect. Don't bother with Tractor supply even though they are a Purina dealer now, they have central warehousing so can't get you the special order fish food.
Uploading some photos will also be very helpful, if its possible.
yuor need to add iron potash magnesium and a little boron and you will se the differenz
Thanks to everyone, for all the great ideas.I went through and tried to check everything everyone was saying. I checked my Ph and it's running in the 7.2 range everything seems to be good except for the water hardness. I'm not sure what difference it makes.
I order my bag of Aquamax 4000. I'm having trouble finding pot ash. But I will find It. Once I get it how do I apply it into the system, and how much without affecting the fish? I had my system between a brick wall and my trailer. It still got sunshine, but maybe this was the reason for my lettuce growing tall instead of wide. So I moved the system a little. Thanks for all your support guys...
potash is an old fashion term for potassium (potash and wood ashes will provide potassium as well as raising pH) You can also get potassium by supplementing with seaweed extract like seasol or maxicrop. The seaweed extract will also provide many trace elements. A cap full of the liquid seaweed extract per grow bed will probably do depending on the size of the grow beds. I have used Murate of Potash (from ace hardware, otherwise known as potassium chloride) when I couldn't get seaweed. I used about a spoon full dissolved under the water inlet to the grow beds.
We supplement nutrient where there are deficiencies. With high quality fish feed, balanced component ratios, target PH/DO levels, these generally provide adequate nutrient for plant growth. If we feed lightly, fish can consume most of the nutrient with very little left over for growing plants. If we have too high ratio of media to fish the same can occur. If we add too much of one type of nutrient it can affect the absorption of other nutrient in the system and present apparent false deficiency symptoms in our plants. If the PH is too high we also see these symptoms even though there is adequate nutrient in the system water.
AP is similar to ecosystems found in Nature and therefore delicately balanced so even little changes have a great effect on them. If we adhere closely as close as possible to suggested ratios and make only small gradual changes with inputs we can create/maintain strong immunity in our AP. Hopefully over time the operator will develop an intimacy with his AP and will intuitively sense what and how much additions are necessary and this is what I'm striving for
I"m dying over here with algae. It clogs everything I find my self clean pumps,PVC and wiping down walls once a week if its hot.,any idea's guys...
Block out as much sunlight/light as you can and don't add any 'supplements' containing phosphorus or phosphates.
Thanks,That sounds good. I have the metal cargo container that they sell on this site (The tote) .I think another problem is that the plastic it white. I also still have a hydroponics system going, with a holding tank that's black, and its never had a drop of algae in 3yrs....thanks again
Yup, whether hydro or AP it's important to block out as much light as you can from entering your "nutrient reservoirs". Those HDPE plastic IBC totes let in a lot of light. This late winter/early spring I used a couple left over bottom 2/3rds (totes after cutting grow beds out of them) to place over top of some 'in the dirt plants'. I half though nothing would grow much under them since there was so little light outside and thought the totes would block out what little there was...(but some frost protection was the primary purpose). Holy crap was I wrong! Everything under the tote was just bursting green. The grass, the plants, flowers...everything! The grass was 3 or 4 times as long under there than outside, and lush green too, not at all pale...so those totes do seem to let through quite a bit of light.
I've got one more question...Do I really need a sump tank? I don't have one right now because I don't know it's function. I know you could grow other types of fish in it. But whats it's original function?