Concerned about one of my gouramis

[Kieflow]

Hello all, over the past day or so one of my gold gouramis has been acting lethargic (spending most of his time laying on a lava rock which is abnormal for him). I was looking him over this evening and discovered what looked like some sort of a scratch or wound on the left side of his head right in front of his gills. I also noticed a small amount of translucent substance coming from his anus earlier in the day that wasn’t there this evening. Shortly after I noticed the abnormality on his head he started flashing for about a minute specifically rubbing the spot on his head. No other fish are exhibiting any of this behavior in the tank. Any help/suggestions are appreciated. 

75 gallon planted tank about 10 months old.

Ph 7.4, nitrates 20 ppm, temp 80F, gravel substrate with about 4lbs crushed coral. Ppm of tank water is 100. 

Edited October 9, 2020 by Kieflow

[Cory]

Have the fish ever been dewormed with something like Paracleanse? 

[Kieflow]

No, however I did order the 20 dose from your website last night. I will probably do the whole tank since none of the fish in it have been dewormed. I have had that gourami for several months now. Is that common for these symptoms to just start now? 

[Kieflow]

18 hours ago, Cory said:

Have the fish ever been dewormed with something like Paracleanse? 

Should I treat the entire tank? Also, is it common for these symptoms to show several months after adding the fish to the tank? 

[Cory]

It's common for internal parasites to become a problem months down the road as they are a slow killer. If you've never dewormed your fish, I recommend treating the whole tank as it is very common. Virtually every fish that goes through a fish wholesaler/store is going to have them unless specifically treated.