Betta Fish: weird algae on tail.!?

I was hesitant to post on here because people are soo mean on here!! i thought i could just do some google searches but unfortunately it wasnt that easy.! But i am literally willing to do anything for my little guy. soo please help just try to be nice about it..

My last post describes his situation a bit better (alot of people were saying it was difficult to understand i do apologize i did type it while i was crying and was just desperate for answers fast!) So i am going to try my hardest to make this as easy for everyone to understand as possible.

Anyways his water levels are literally perfect🤦‍♀️ which is so irritating because atleast if they were bad i could just do a water change, but no of course not..

Secondly, i am extremely broke and cannot afford any real plants he has 2 very scrawny plants im not exactly sure which kinds tho (im sorry!! the employees said they were good for bettas tho, then again it was petsmart..) But!! if this is a major issue i will do absolutely whatever i can to get him some new plants as i am 17 and will probably just pester my grandpa for them.😭

He does have a heater(80*f) and a filer, as you can see in the video his filter is quite too strong for him my old one broke like 2 days ago and had such a weak stream of water coming from it so i got the new one and unfortunately its too strong. I am going to replace it ASAP tho so hopefully thats not an issue. Ive also been unplugging it at night and adding a little seachem prime to the water.

I have also been giving him a bit of stress zyme each day because i seen it recommended in another redditors post. (Please let me know if i shouldnt be doing this, im only 2 days in, google said it was okay but google isnt ALWAYS right.

Anyways like i said theres alot more explained in my previous post (not the one about the heaters lol!) But i still wanted to include some info about his current situation, As you can barely see in the video he has like dark fuzzy i think algae on the end of his beautiful tail.!! and i dont know if this is a bacterial infection or a disease or simply just normal.. but how do i get rid of it regardless?

Again please be as nice as you can with tolerating me, my post, and my poor guys situation.! but then again any feedback is appreciated.!! If theres any information that i left out that is necessary let me know and ill reply as soon as i see your comment!!