I seriously doubt that is your problem. Have you checked your co2? This is
more than likely the source of your algal bloom. I too have cracked a
light
into the tank and never experienced any blooms or adverse effects, and
that
was on a 3 footer. Are you using DIY co2 or do you have a cylinder? Either
or, add more diy bottles or crank up the pressurised container. also very
important, keep your surface agitation down to a MINIMUM. Do your plants
pearl during the day? If not I doubt you're getting enough co2 into the
water column. IME, a hefty dose of phosphate will only perk things up a
bit
not cause algae blooms, this just seems to be another aquaria myth...

Depends on what you define as hefty.

I was running over 4ppm and I've been told to keep it under 1ppm.

I've got DIY co2 happening and the little JBL co2 indicator is showing max
level of saturation now.
How accurate are these?

Plants are pearling now I've adjusted the Nitrates.
Having the iron levels at zero probably wasn't helping either.

What sort of phosphate, iron and co2 levels should I be looking to achieve?

K