Anhel, Excel is a CO2 supplement. It's not harmful to fish and is used quite frequently in NPT's to keep algae down and the plants growing
But the algae we have cannot just simply be wiped unfortunately, much of it is blue-green algae which is actually a cyanobacteria and is toxic to fish if eaten so most fish don't eat it, nor do snails. But it's on the plants and algae build up will block the light from the plant causing the plant to die which is not the goal in NPT tanks. Plant death equals ammonia spikes so that's not good! By adding Excel, the only thing that's being added back to the tank is CO2 which is originally in there in the first place, just a lower concentration of it is all.
Stress-Zyme is a beneficial bacterial supplement, basically the bottle of good bacteria. That's just added to keep the tank healthy with good bacteria. However that one is not needed once the tank is established, so Phantom you can stop using that now in case it is linked to the girl. I doubt that it is since I've used to plenty myself but it might be worth it. You've got plenty of good bacteria in there already
Use it if you rinse out a sponge filter or filter media or clean out a filter, otherwise you won't need to use it on an established tank.