should I be concerned?

[intarsiabox]

Any livestock missing? It doesn't take much to raise phosphates in a tank.

[molotov]

what are your water parameters? Are your nitrates creeping up?

[MMAX]

RO water? If so your filters might be in need of a change.

[Enigma]

Can you provide photos of the algae?

While it is true that many GHA issues can be resolved by lowering the nutrients in the system, there are some that are able to grow exceedingly well in lower nutrient environments: bryopsis and debersia, which are both green "hair" algae being two of them (though bryopsis is the more difficult of the two to get rid of).