I've seen a fair bit of discussion about using Maxicrop with and without iron, but I didn't see any rule of thumb for how much to add. My system is cycled and established, I just need to add it to give my plants a boost. I have 160 gallon tank with 1-3" goldfish and a 85 gallons of growbed. I'm wondering how much to put in at a time. I've got a whole gallon bottle of Maxicrop plus Iron. Is there a ratio to use based on tank or growbed volume?
My plants are doing relatively well, but some are starting to show some signs of yellowing due to iron deficiency (and perhaps other trace nutrients)
If someone has already answered this, please point me in the right direction. Thanks!
Here is a link to almost the same question.
and there is a quote of my reply
Well fish foods and source water does not always contain everything needed. Potassium is commonly supplemented as is Iron depending on your pH and source water.
When supplementing with Maxicrop I usually recommend reading the bottle. I will probably have a recommendation for an amount to add to some amount of water and then spray over some square footage of growing area. It is not the amount of water you are interested in but the amount of growing area. So say they recommend using like 1 oz of extract mixed in water and used to feed say 100 square feet. If you have 100 square feet of growing area, then add that 1 oz to your water. Now these numbers are only an example please read the bottle I don't have one in front of me and I don't remember the exact dosage. Now if you are seeing the deficiency in the raft bed the I would add the extract to the raft bed. It will mix all over the system and turn your water tea colored but the fish generally don't mind that.
Now many people have found that they need to supplement more heavily during the first season and then in later seasons have found they don't need to supplement at all. The quality of your fish food will greatly affect how much you may need to supplement as will your source water. If you are feeding cheap pond diet or goldfish flakes, you may find you have more nutrient deficiencies in your plants than if you feed a high quality dense culture feed for recirculating aquaculture. See the pond diet sorts of feed are designed to just get a little extra growth from fish that are otherwise mostly eating a natural diet from the pond and therefore are not really complete feeds. The Goldfish flakes or other aquarium or ornamental feeds are designed to keep the fish alive while providing the least nutrition possible so that aquarium and pond keepers can get away with the least amount of water changes possible which is kinda counter productive for aquaponics.
I don't recommend adding supplements all the time, only when you plants show they need it.