Got yellow leaves?

I transplanted garlic, basil and parsley last week into my Barrelponic systems. Within a couple of days, the parsley leaves and some of the other plants started to turn dull yellow. Also, I noticed some of my other plants had stunted growth. Uh oh.

Maybe the sea salt I added to the water (to cure some sick fish) the previous week was killing my plants? Plants don't like salt that much. But, I hadn't added that much salt. After a little research and a quick water test, I suspected that the slightly high pH of my water was causing Iron Chlorosis. Iron Chlorosis is a condition where plants are unable to extract sufficient iron from their environment, due to high alkalinity. The leaves turn yellow and eventually brown.

Chelated Iron may be added to counterbalance high pH and reverse the yellowing process. Because it is safe for fish, it is widely used in Aquaponics. But, Chelated Iron can be expensive, so some Aquaponic farmers add rusty nails or rebar ("pig iron") into their systems instead. Rust is really iron oxide, which is not a water soluble form of iron like Chelated Iron. Rusty nails turn the water brown, but plants can't the absorb iron oxide into their cells. Also, most nails are made from a mix of metals anyway, so you have to be careful that you're not adding other unwanted metals into your system as well. 

Since Chelated Iron seems to be the most widely recognized supplement for Iron Chlorosis, I thought I'd try it out to save my yellowing plants. I found some tablets in powder form in the dietary supplement section of a local supermarket. They were only $5 for a bottle for 100 tablets, which was much cheaper than what I expected. Unfortunately, you get what you pay for. The tablets must not have been very pure, because not all of the powder dissolved into the water. I found a few dead fish the following day. I suspect they ate the undissolved additives such as potato starch, magnesium stearate, and medium chain triglycerides. Potato protein is found in my goldfish food, but the other stuff is not. A purer form might have saved the fish.

The good news is that all the plants responded well. The leaves returned to a vibrant green after a couple of days. Here's the parsley after Chelated Iron treatment. Growth is strong once again.

So, what's the lesson?

Be careful what you add. Unwanted chemicals can quickly harm your systems. What's good for your plants might not be good for your fish, and vice-versa.