I am getting fed up with fishkeeping as nothing seems to go right for me. I have a 300liter tank (48"x20"x24") which has been set-up for around a year now, I do weekly water changes (with dechlorinator) of around 70 liters along with gravel vacing and alternate week filter cleaning (I have 2 big filters on it, 1 internal fluval jumbo and 1 external fluval 304) one week I clean the internal and the next i clean the external and so on. Its a planted tank with DIY Co2 and the plants are growing fine. Dispite all my best efforts at tank maintenance, even at this point in time I have multiple diseases in the tank and its really getting me down. Some of the fish have white spot, some have fin rot and some have some kind of white fungal growth, and ontop of all that I have some wierd 'worm' things living in my gravel. The livestock in the tank are :
2 angelfish
2 clown loaches (2")
4 african butterfly cichlids (1-1.5")
2 blue acaras (2")
2 ottos
2 swordtails
7 herlequins (altho i suspect one has died as I havent seen it for a while)
8 rummy noses
2 neon tetras (again I think one has died)
2 bristlenoses
2 apistogramma agassizi
1 jade eye cichlid (is that the same as blue eye cichlid?) (2")
As u can see the tank is deffinatly not over stocked as they'r all small at the moment, and even when they'r fully grown that will be an ok tank stocking level yes?
The water parameters are pH : 7.2, Ammonia 0, NitrAte 0 most of the time, NitrIte 0, GH 7, KH 3-4. and tap water is the same but with pH 7.6
I have tried treating with melafix which didnt seem to do much and also have tried a white spot treatment and raised the temp to 82F (normally 79F) which seems to have helped somewhat
Can anyone see what i'm doing wrong here?

2 angelfish
2 clown loaches (2")
4 african butterfly cichlids (1-1.5")
2 blue acaras (2")
2 ottos
2 swordtails
7 herlequins (altho i suspect one has died as I havent seen it for a while)
8 rummy noses
2 neon tetras (again I think one has died)
2 bristlenoses
2 apistogramma agassizi
1 jade eye cichlid (is that the same as blue eye cichlid?) (2")
As u can see the tank is deffinatly not over stocked as they'r all small at the moment, and even when they'r fully grown that will be an ok tank stocking level yes?
The water parameters are pH : 7.2, Ammonia 0, NitrAte 0 most of the time, NitrIte 0, GH 7, KH 3-4. and tap water is the same but with pH 7.6
I have tried treating with melafix which didnt seem to do much and also have tried a white spot treatment and raised the temp to 82F (normally 79F) which seems to have helped somewhat
Can anyone see what i'm doing wrong here?