They, Seachem, appear to claim it doesn't.

Maybe your water changes? Check your tap.

Twice a day, until "a couple of flakes to make it to the
substrate" sounds like overfeeding - unless you have bottom
feeders. Feed once a day, exactly what they will eat -
completely - in 5 minutes.

If you dose Flourish and see noticeable up tick in algae,
then you and your tank may not agree that you're limiting
its growth with phosphate. As I recall, Flourish doesn't
have nitrate either, so you may be limiting on something
else. Plants need a dozen, or so, things. Limiting any of
them will alter growth patterns in various ways.

I use PMDD. I can force my green spot algae two ways.
First, if I does even a tiny amount of P I get a sustained
expansion. Played that fool exactly once - and learned my
lesson. Second, if I massively overdose the PMDD (a 10x
dose) I can force a couple of day spike.

Flourish should be fine. At least they publish their specs.
They have allot of stuff in there that probably doesn't
mean much to your plants, but probably doesn't hurt anything.

From their website:

Guaranteed Analysis: Total Nitrogen (N): 0.04%; Available
Phosphate (as P2O5): 0.0100%; Soluble Potash (K2O):
0.0600%; Ca (Calcium): 0.1736%; Mg (Magnesium): 0.1154%; S
(Sulfur): 0.2773%; B (Boron): 0.0096%; Br (Bromine(as
bromide): 0.0001; Cl (Chlorine(as chloride): 1.15%; Co
(Cobalt): 0.0004%; Cu (Copper): 0.0001%; I (Iodine (as
iodide)): 0.0001%; Fe (Iron/Ferrous gluconate): 0.3886%; Mn
(Manganese): 0.0125%; Mo (Molybdenum): 0.0015%; Ni (Nickel):
0.00036%; Rb (Rubidium): 0.0001%; Na (Sodium): 0.0743%; Sn
(Tin): 0.000030%; V (Vanadium): 0.000030%; Zn (Zinc):
0.0004%; Arginine: 0.016%; Glutamate: 0.09%; Lysine: 0.03%;
Tyrosine: 0.019%; Choline: 0.0004%; Inositol: 0.0011%;
Biotin: 0.0004%; Niacin: 0.025%; Pantothenate: 0.0070%;
RiboÅavin: 0.0020%;Thiamine: 0.0020%; Vitamin B12: 0.00009%;
Vitamin C: 1.0%

********************************

nemo wrote:

I do at least 1 x 25% water change a week

I fertilize twice a week with Seachem Flourish.
I find that brush/beard algea get a boost on the Java fern and dwarf
hairgrass leaves everytime I fertilize with Flourish.

I feed the fish twice a day but just enough for a couple of flakes to make
it to the substrate (the rest is consumed at the surface or the way down).

Should I be replacing Flourish with something else?