In message , Altum
writes
The name Sequestrene was familiar enough that I got curious and went
searching for it in the aquatic plant forums I frequent. Turns out
there's not much information at all. A few Europeans mention using
EDDHA-iron in aquariums, and nobody has said it killed their fish. It
could certainly be a dosage thing but that label is pretty scary. :-/

I found a lot of mention of Chempak Trace Elements from UK aquarists.
The Chempak mix has the cheaper, more common EDTA iron. Maybe you
could find that brand since EDTA chelates are a bit more tried and true.
Chempak have three chelated iron products as stand-alone items, the one
tagged for pH 8+ is EDDHA, which is what I use. Even at 0.1ppm iron
dose, it colours the pond water for a few days.
The aquarium iron test kit I bought recommends 0.25ppm iron ISTR.


Iron/mangnese shortage is hard to miss. The plants get chlorotic with
pale or yellow tissue between green veins. I'm still learning to grow
lilies myself so I hope someone else can help more with the
troubleshooting.


--
steve