Guppy Tail Rotting?

[Frostfire]

Just trying to figure out whats wrong with my little blue guppy before he bites the dust, preferred he if didnt
 
Ive had him for 6-8 months now, hes in a 10 gallon tank with 1 other fish and a Chinese algae eater, used to be a third fish but he died off 2 months ago. Was 2-3 years old not quite sure what the fish species was. All of my fish are from pet smart, once my last 3 pass away i have no intentions to buy more as i do not have the equipment to keep them humanely.
 
But for my guppy hes been fine until the last month and a half where he has started developing what i expected was fin rot. I gave him the regiment, dosed the tank with tetra cycline, and then followed with melafix to heal the tail. However nothing happened, his tail only continued to get worse. So i took everyone out, did a full wipe down of the tank with bleach, then put everyone back in, and tried the tetracycline and melafix again to no avail.
 
At this point im assuming its either due to poor water quality from overfeeding or the other fish a neon striped glass fish is nibbling on his fin. Ive looked into other possible fish diseases but nothing really matched his issue other then fin rot, however i could be wrong.
 
An accidental leak from the fish tank lead to me doing a full water change and cleaning of everything, im hoping he survives the cycle as i do not own another tank to put them in while the tank cycles, i only have a small fish bowl i keep them in when i gravel vac the tank or do a large water change.
 
Our tap water is very hard so its possible that could be the issue, but im posting her for second opinions as to what might be wrong with him, and if anyone knows how to possibly soften tap water without a reverse osmosis system.
 
http/dropcanvas.com/88v20 some pictures of the guppy in his fish bowl(i was cleaning the 10 gallon tank)
 
 
 

 

[LyraGuppi]

My only idea is that is could be the Chinese Algae Eater, who turn carnivorous when adults. Now sure though.

 

[Frostfire]

the algae eater never leaves the side of the glass, ive never him interact with the other two fish ever during the year we have had him. If anyone is nibbling its the neon glassfish and i have seen him chase the guppy, but not very often.
 
Im assuming its just chronic poor water quality, i just did a fresh 100% cleaning, so if he survives the cycle he will recover. Im hesitant to buy more anti bacterial products until then unless someone knows whats what with my guppy.
 
i didnt add water parameters to the original post as my tank has just been freshly cleaned but before it was cleaned it was something along the lines of this (i only have the jungle quick strips from walmart unfortunately for water testing)
 
Ammonia - .25-.5
Nitrate - 0-20
Nirite - 0
Total Hardness - 300ppm+
Alkalinity - 300+
pH- 8.4+
 
He acts sort of normal in terms of eating and swimming, he does spend alot of time swimming near the top or near the filter.
My mom took care of the fish before i started caring about them so im unsure of water changes up until the last 8 months or so, but i try and change the water at least twice a month. Since he has gotten sick i do a 50% change once a week.
 
Ive used Melafix, Stress Coat, Tap Water Conditioner, Tank Jump start and tetracycline on the tank in terms of medication. As well as the Ammonia Clear and pH balance tablets, which seem to have zero effect on the water, so i no longer use them, but they were used on the tank before the cleaning occurred yesterday.
 
Its a 10 gallon tank
 
The newest fish is the guppy from 6-8 months ago