Aquaponic Gardening

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I have not had much luck growing corn for some reason. It starts out very well gets about a foot high then the bottom leaves start turning brown and dieing. I have corral pieces for calcium, add iron to the bed which is a little over a year old now. The water is a very nice amber color and my goldfish are getting the size of small koi. I also do not have luck with lettuce. I have basil, okra, green beans, squash, brocoli, cherry tomatoes, radish, plus green grapes, two avacodo trees, date tree, a succulent of some kind and a brain cactus. The ph is 6 and I have nothing to measure ammonia or nirates with. Any clue? Also it is indoors with temp between 75-80F and gets both sunlight and grow light. The substrate is a mix of hydroton and large perlite. Flood and drain system. I have never added seaweed extract to the system either.

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I think i will just top the water off and add some limestone and see what happens then. I have plants that are growing very well, like my grape plant, basil, sugar baby watermelon, the green bell pepper is growing very well, just not the flowers and squash is trying to over take the bed, but all the little flowers suddenly turned brown and died. The green beans were doing well with green beans on them and they also turned brown veined and leaves starting drying up and dieing. This is also an indoor growing unit. Okra and cherry tomatoes are growing painfully slow. My avacado trees growing well, date tree doing ok and my one corn plant left is doing ok except it wants to lean in one direction. I will use just a little bit of lime due to such a small system and watch for a while. I really thank everyone for responding and helping me, it is really appreciated.
Shells are a buffer but only a slow buffer. A single shell in a grow bed is not going to have a big effect on pH. You may need to add a bit more buffer material to keep the pH from dropping too low in the future. Get a bag of grit like is used for laying hens and you can add small amounts of that to your system to help buffer the pH or some garden lime added in small amounts could help too but you don't want to raise it too much if your ammonia is high. I agree with Kobus.

As to water changes, I would only do them if the ammonia or nitrite are in a dangerous range for the fish and your source water is good.

Just a warning about tap water and pH. Directly out of the tap, the water could be giving you a false low reading since water in pipes or from a well or from a pressure tank will often have lots of carbon dioxide dissolved into it which acts as a mild acid. If you bubble the water overnight and take the pH reading again, it may be far higher than you thought. This trivial bit of knowledge came to me late after I struggled big time trying to figure out why my tap water (which directly out of the tap read 7) would cause my hydroponic system pH to keep rising above 8!?!?!! Why the heck would topping up something that had a reading of 7 with something else that had a reading of 7 cause the pH of my nutrient mix to be up over 8 the next morning?!?!?!? Well quite simply, my tap water actually had a pH of 8.2 after the dissolved CO2 escaped, I just never new to bubble the water before taking the pH reading to know the real story.
By bubbling you mean sticking a air line bubbler in the water? I thought I might better check this just in case. I have a bubbler in my FT that I keep going all the time.
Yea, basically you just need to make sure the dissolved carbon dioxide has time to escape from the water so you can get an accurate pH reading. Easiest way to do this would be to put an air stone in and let the water bubble for a while.

It is good to have aeration for the fish tank as well.
Personally didn't use trace elements as i cycled with homemade seaweed extract. I did however have to add iron chelate about 1/2 teaspoon for 50 gal growbed. I'm interested in what type and how much trace did you add? I've read that tomatoes require more boron and molybdenum than other types of plants. Can you shed some light as a matter of interest? Also do you know if trace elements affect fish in any way?

Kobus Jooste said:
Just a quick update. My three sweetcorn plants are over two feet now, and no signs of browning, but some signs of nutrient issues. The system is a bit new, and there are a bunch of tomatoes that may be stealing the trace elements. Just topped up on Trelmix today and we will see how the corn responds
Aloha
One thing Murray Hallum does with an acidic pH is put egg shells in a nylon stocking and put it in the gravel bed. It brings the pH up. My WWOOFer has been running an experiment.
she acidifys the water in a bucket with lemon juice and then puts the egg shells in. You would be surprised to see how the pH will return to 7. I think adding things like this is less drastic than dumping chemicals in. We really only know what the true pH is if we have a calibrated pH meter.

If your system really does stay stable at a pH of 6.5, that is actually really great! Most plants should like that much better and if you can easily maintain that pH without danger of it dropping way low and crashing the bio-filter, the tilapia are probably fine with it. Rain water usually does need some regular lime to help harden it a bit.

I find my systems if I heavily buffer them with shells, I am stuck with a pH of 7.6 or higher long term and if I don't heavily buffer, the pH will be trying to go below 6 and require me adding small amounts of lime daily. When I added enough chicken grit to keep the 300 gallon system from crashing while I'm too busy to be checking it daily, It is back up to 7.6.
Ah well.

Different source water will have a strong effect on your start up and how much buffer or lime you need long term.

Kobus Jooste said:
Sometimes systems can be very persistant about pH. Mine flatlines on 6.5 and there are about 2 cupfulls of lime and multiple additions of potassium hydroxide having been added and still no shift (Whole system water volume only about 1200 - 1500 liters). Anyways, it seams to be alright for the plants in my system.

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