Backyard Aquaponics
A place to discuss aquaponics

Hello to all pros... am still a noob and just wanted to confirm that there is an iron deficiency based on attached photo?

System is cycled but is relatively new

pH ~ 7.0
Ammonia ~0.5
Nitrite ~0.5
Nitrate ~50

I input about 30g of chelated iron (eddha) a few days back, and colour does seem a little better (pic provided is taken today).

I also foliar feed seaweed extract about once a week.

Just wanted a second opinion before I add more Fe as its easier to add more if insufficient than having to make changes after adding too much.

It's not an iron deficiency, that would cause the new leaves to turn yellow, not the old ones.

Nitrite looks a bit high. If you have fish in the system, I would stop feeding until it goes down and make sure that you have the water salted to help them with nitrite toxicity (it's 1 part NaCl per thousand total using water). Strawberries don't like the salt and if you're planning to grow these you may want to skip the salting.

Looks like it might be a magnesium deficiency (lower leaves affected with yellowing between veins). Might want to do a foliar spray with epsom salts, the instructions are usually on the container - I think it's 1 Tablespoon per gallon of water but check around because I'm not sure my memory is right on this.

Hmmm will try the epsom salt and revert again on the results. Usually how long will it take after application for colour of the leaves to be restored?

As for nitrite, i tested using a sera kit, which shows results for 0 than 0.5. And test results always flunctuate between 0 & 0.5 (it increases then drops back on its own) so i am guessing this is ok? Or does the system have insufficient nitrifying bacteria to keep up with the ammonia input thus the lag?

Another question - The label on seaweed extract I use states that both potassium & magnesium are available. I foliar feed seaweed about once a week. Is magnesium not readily available to the plant in foliar applications?

I'm not certain how long it will take but expect that you'll probably see results within a couple of weeks.

Yeah that's probably OK but watch the feeding levels, especially if this is a new system. Typically the conversion from nitrite to nitrate goes pretty fast and you don't see any nitrite when you test. If this is a new system and the filter's not been going that long then yes it could be because the bacteria haven't built up enough. New bio-filters are pretty sensitive and are more prone to fluctuation that ones that have been established for at least 6 months (although I'd still consider 6 months to be pretty new).

Basil has a high requirement for magnesium and would probably make a good indicator plant for low magnesium levels in an AP system. In addition other nutrient components of the system can affect how much magnesium is actually available (like calcium and potassium which compete for uptake when they are all in the system water together). This shouldn't affect your spray applications though and you should be getting some magnesium through those applications.

I don't know the specifics of your system or seaweed supplement but many systems get enough without supplementation because it's in their top up water and feed, in sufficient quantity. Spray applying it as you've done with the seaweed extract should help but I'm pretty sure your plants aren't getting enough based on the foliage and the fact that basil needs more than most plants.