Herbs - First true leaves turning yellow

Hi all,

I have a homemade aquaponics setup on my countertop. Everything has been going well until recently. My herbs just got their first set of true leaves and they’re turning pale yellow and weak. I am growing parsley, cilantro & basil.

Nitrate levels are 20ppm or below.
Nitrite & ammonia 0.
Water hardness 75 (soft).
Chlorine 0.
Alkalinity low.
pH 6.8.

I have 4 fancy guppies with a pump to transfer water from fish tank to plants above and then gravity returns the water to the tank through a small hole. There is also an indoor grow light on the plants 12 hours a day.  The plants are in a clay media setup that stays full with water at all times. (I tried draining occasionally to mimic a bell-siphon setup but that was disrupting my nitrogen cycle). I’ll attach an image here of my parsley showing how the first true leaf has been getting more and more yellow. Thanks so much for your help with this!


- Dianna

Hi Dianna,

Welcome to Permies.

Thanks so much John any advice for my herbs?

Here’s a closer up of one of the yellow leaves if that helps:

Dianna, welcome to the forum!

What have you tried? Iron? Reducing the amount of water?

Since some of them look leggy, maybe the light is too far away or not enough?

Hi Anne,

When I saw the cilantro and parsley getting leggy, I did move the light closer to try and help them. Since the yellowing has started, I’ve added an air stone to the water plants sit in and Ive also elevated the plants a touch out of the water to make sure the roots aren’t completely submerged. Just recently I moved the light away to see if that helps at all. Havent added any additional nutrients to the water since I am not sure which, if any, are needed here.

Hi Diana,
Unfortunately, I am a long way from being an expert in gardening.    Sometimes I do have great crops …..by accident.

Most likely, it's interveinal chlorosis caused by a nutrient deficiency.  Usually in aquaponics, it's iron and it can be corrected by adding chelated iron.  That sounds pretty easy, but there's different kinds for different pH levels.  For your pH, I'd use 11% DTPA iron chelate.  It might take just a pinch.  You can also use some sort of kelp extract like Maxicrop.  I'd try to bump up your nitrate to around 40 ppm by adding more fish or reducing plants.  Some crops like basil suck up magnesium like crazy.  This can be corrected with epsom salts.  To reduce your dependency upon supplements, try to increase the aeration in your system to promote the break down of the fish solid waste in the media bed through remineralization.