I think phosphate is hard to remove, especially once introduced... if it's
not in the water, it probably has attached to something in the tank..
driftwood or substrate.... maybe even the plants...

I'm running a JBL phosphate sponge in the canister filter and even after a
day it has reduced the levels.
The Iron level was also at zero so I'm thinking it would also be stunting
the plant growth.
I'll give it a week or so and see what happens.
Short of that I'm thinking of tearing down the tank and starting with new
substrate.

K