Backyard Aquaponics
A place to discuss aquaponics

Hi guys

I have held off posting this for about a year now as I have played around with my aquaponics system but I just can't get it going properly.

This is an IBC system I built in my classroom with a 600W HPS bulb. I am not sure what the deficiency is that is stunting my plants growth so much and would love some help.

The system currently only has one fish in it - an Australian Bass - but it's big - approx 1.2kg

Plants have curled leaves, discolouration and are dying at the tips.

I have been occasinally dosing the system with worm wee/seasol, urea to increase nitrates supply (no ammonia or nitrite present in the system - tested weekly) and have just started dosing with iron chelate also

Photo's of plants and system:

System:



Chili plant:



Fennel: (Yellow leaves)



Marjoram:



Chives: (dead tips)

Hey there,
Are you showing nitrates? If so then it sounds like a potassium deficiency. Depending on pH, you can add potassium hydroxide(if low pH) or potassium sulfate (if high pH). You won't need to add a lot - I would suggest a tablespoon or two in the growbed.

--
Eddie

Just realised the pics arent working...

Chili



Marjoram



Chives



Fennel



System

Hi ebeuerle

I don't have a nitrate testing kit but it seems like something I probably should invest in!

I can certainly get those chemicals directly from our school chem store if you think they will do the trick, pH is currently exactly 7 (using a pH probe). Not sure which you would suggest I might use?

It looks like calcium in the chillie plant and the chives have the growing tip dead so maybe again calcium,as for the marjoram i am not sure,is it just the older leaves that are showing the cholorosis ? are any off them falling from the plant ? it doesn’t look like Potassium as there is no scorching on the margins in fact there looks to be no necrosis on the leaf either.......

It definitely seems like a lack of nutrients, particularly nitrates. How much fish feed are you feeding the fish with?

What timings are the lights on for? Lights on for 18hrs/day with an MH globe would be best for the plants at this stage, but I guess the bright light is hard in a classroom with children around.

Yeah I said potassium based on the plant descriptions since photos weren't loading. I agree it looks more like nitrate or calcium. So I would highly recommend getting a nitrate test kit. Also if you want to try supplementing calcium, use calcium chloride and spray it as a folar supplement(1 tsp/gal to start). That shouldn't raise the pH and should show quick results.

I look forward to seeing the answers to the other questions folks have asked...

Thnaks for the help guys, answers to your questions:

- is it just the older leaves that are showing the cholorosis ?

No, they just show it the most. All leaves have at least some discolouration and many are brown/dried out/dead at the tips, especially new growth

- are any off them falling from the plant ?

yes, all plants actually are losing leaves quite regularly, the chilis for example lose a leaf most days, and usually not the oldest leaves...

- How much fish feed are you feeding the fish with?

The fish is fed on a diet of compressed dried blackworm cubes and freeze dried shrimp. It has not been eating much this last week, but typically is fed 6 1cmx1cm cubes a day and a handful of the dried shrimp. On top of that the students usually feed it 7-8 worms from the worm farm every other day


- What timings are the lights on for?

As you say, can't really run it during class, so I have it running on an 15hour cycle from 4pm till 7am. I could extend that further if you think it might help?




I'll mix up some calcium chloride foliar spray now and give that a go. Again, thanks for all your help, I have been reading and tinkering as much as I can but really need this direct info, it's much appreciated!

Hi again, the feed sounds too high on protein, unless you are looking for rapid fish growth aim for 35-40% protein.
If the grow bed is getting fluorescent light and some sunlight during the day there is too much light for the plants and they are stressed as well as nutrient deficient. Can you turn the lights off for 4-6hrs a night? Light on 4pm, off 10pm, plants sleep, then lights on 4am until natural light for the day cycle.
Also you can foliar spray Bloom Seaweed or Seasol Powerfeed at low concentrations. This will help destress and provide important minerals.
It wouldn't hurt adding some iron and potassium regularly too.
Good luck!

PS foliar spray when the light goes off at 7am for the day cycle... not before the HID light goes on in the arvo.

Cool, Ok thanks for the info, I will adjust the timers to allow a "siesta".

The fish diet is limited by what the damn thing will eat! It's very fussy and I haven't found many other things it will eat, even if it is without food for extended periods of time. Not sure how to manage that one.

I will foliar spray every morning, what consititutes a low concentration? Say 50% of the recommended dilution?

I am dosing with iron, does anyone know what chemicals I can dose potassium with safely? I have a huge supply of chemicals here that I can access for free and would prefer to use the lab compounds if I can

Cheers!
-Tim

Potassium hydroxide / carbonate / bicarbonate will provide potassium, but you would use them all differently as they have different affects.
I don't have experience with seasol as a spray, but up to 5ml/l should be safe. You would use bloom seaweed at a concentration of 2-3ml/L and add 10-20ml /week to the water if you can't change the fish side of the equation!

To quote Eddie



And I really must get some of both for my war chest ..
..
.

If pH is spot on I'm guessing a little of each then, cheers!

If i remember your PH is 6.5 i would keep it there by dosing with Potassium Sulphate, one teaspoon per 1000 litres per week,the other two will raise your PH if this is what you want to achieve.

Cheers, when dosing should I make a solution or simply mix into bed as a powder?