Backyard Aquaponics
A place to discuss aquaponics

Dear All,

My AP system has been running stable for 7 months, the fish is healthy but the lettuce doesn't grow well as expectation, they still very little after 3-4 weeks. I thout it is due to low NO3 level

I measured the water quality:

- NO3 = 0
- pH= 7.6

Please help me how to increase the NO3 level in my system

Thanks a lot

Regards,
Tinh

Hi Tinh

How big is the fish and what are you feeding it with? Most people use a commercial pellet type feed designed for growth not just maintenance. You may be able to feed you fish more if you do multiple smaller feedings during the day but watch your ammonia and nitrite levels just in case. It's not uncommon for systems with very good growth to have a zero reading for nitrates. What I'm trying to say is that this might not be a nitrate level problem or it could be nitrate levels along with something else.

You may have a lack of nitrates but I think you're looking at an iron deficiency as well, are you using chelated iron or any other kind of iron? If you are, how much and how (spray or to system water) are you adding this (if you are)?

Cheers

On top of what Scotty said, how much light are the plants getting?

@Scotty:
I'am using commercial pellet type feed the size is suitable with automatic fish feeder, i have tried to adjust the amount of pellet so that the fish consumes all in 10 minutes

I don't use any kind of iron. To be honest, i don't know what is purpose of the iron and what type of iron should i add in. please advise further on this and how does it effect to the whole system

@ Colum Black-Byron
the sunlight is all day.

Thanks All!

Iron is used in Chlorophyll production but if it isn't available because of the pH of the solution the plant can't do this. Iron is not a mobile nutrient so you get a chlorosis (or yellowing) of the leaves at the top of the plant (young leaves) while the older leaves stay green. Chelated iron is more plant available at higher pH's but it depends on the type of iron chelate.

Nate Storey has a couple of good videos explaining this -

https://www.youtube.com/watch?v=E4_hCAnymFw

https://www.youtube.com/watch?v=qczagOJG5mI

Probably Fe-DTPA (one form of chelated iron) would work the best at your system's pH.

Thanks Scotty

i can't find Fe-DTPA here in my city
i intend to use one growbed to compost the kitchen waste as organic fetilizer for the plants

Has anybody tried this way to support the plant?

Have you thought of doing a worm compost bin? Then using that compost in your system, as a compost tea perhaps.

Blood meal contains iron and would probably be a good alternative. It's also high in nitrogen. Some of us use a combination of blood and bone meal to keep a system going well when the fish load is too low.

50 gm/ 1000L of grow bed media for the combo of blood and bone when you don't have enough fish to run the system but. You'll wan't to figure how much to use if just using the blood meal alone. The nitrogen content of blood meal could potentially cause an ammonia spike (no one that I know of has had this problem so far) so dose with some caution.

The kitchen waste idea sounds interesting. I think it will either work or you'll have lots of plant problems with things like root rot and other diseases. I like FF's idea a bit better. Then you could feed the worms to your fish too .

Thanks for advices

i'll try with kitchen waste originated from Botanic first and grow the worm in that enviroment. Worm's waste will be a good source for the plant

Does it work?

will update after 8 weeks.