Here’s FeEDDHA. It’s a red powder and turns the water a red-ish iron hue colour, which is the only down side. It’s great for new systems, as it’s stable upwards of 9.0pH.
FeDTPA is a yellow-ish, and now that your system is lower pH, this might be a better choice. The problem is Dealzer & Amazon don’t carry this product, and you’ll have to search other sources. FeDTPA is stable upto about 7.5pH.
NEVER USE “FeEDTA” in aquaponics. I mention this as its the most common form of iron for growing. FeEDTA is only stable upto about 6.3-ish.