If you're talking about green spots algae (GSA) impossible to remove, this is sign of healty tank I've heard.
You must know algae is not nuisible, and is good for the system, but only looks ugly. The best thing I know to remove green spot algae, is with a new razorblade attached to a kind of thing like that.
If it still not work, you might consider bleaching the tank, but by experience, I can tell you're better to tolerate them than bleaching, as it causes a big mess !
In my planted tank, I keep weekly cleaning the front glass, and I don't care for the back glass, this add colors to the tank. I clean it once per 2-3 months, and I don't care about the little greenspot remaining at the end.
Personally, when I clean with this sponge (with the green side), with a lot of force and patience, green spots finish to scrape off.
(Make sure the green of the sponge is not made from metal, but from plastics).
Use a new one that you dedicate only for aquariums uses, aquariums won't tolerate soaps residues.
Also, depending on your photoperiod, you could probably reduce the lighting time, reducing the algae growths. Or maybe add a CO2 system, but this might not be usefull if your light is not strong enough.
I personally like the product "Seachem Excel" that simulate CO2 injection for killing algae.
Maybe adding fast growing plants like vallisneria to compete the algae could help ?
What's your photoperiod ?
What's your lighting system ? Watts, color (in kelvins), type (T8 or T5HO or T5 or LEDS...)
Are you dosing ferts ?