For that you probably want something stronger. I think one of the Maracyn meds treat fungus and are safe for cories. More potent too.
Clean water is a need as well.
He -looks- fairly skinny and clenched, it appears from that photo he has more than a fungal problem. The forehead was likely an injury that got infected and grew fungus, but the rest is also an issue. Are you feeding him more than just algae? They are catfish and need proteins too, like brine shrimp, mysis, glassworms etc and fresh veggies.
I can see you have the wrong substrate and decorations LOOK like they may be rough. Gravel and rough decorations will scrape at their barbels and scales, opening them up to these problems, so if he continues to scrape on them, it's likely the fungus will get worse.
Do you have him in a proper group? He needs to be kept with at least four others, without a proper group they can get stressed and depressed. Stress can also damage the slime coat and cause this problem, especially without proper substrate and decorations. Substrate is better as sand or very smooth, rounded rocks, decorations need to be smooth(rub pantyhose across them, if it grabs it's too rough). Armored though they are, they eventually take damage and get fungal infections like this, they can also get internal damage from hitting their bellies on gravel. So make sure all is proper for them or the problem will continue to get worse, even with treatement that is successful it'll just happen again.