Very Sick Oranda

Question
PLEASE HELP! I am sick with worry over my very ill oranda. Everywhere i go i get conflicting advice and i'm so stressed and he is so poorly. A week ago i noticed a large sore on the side of his body.... The day before i had noticed him "sitting" on the heater so i assumed it was a burn off the heater. I got a heater guard and added melafix to the tank.  

A day  later i noticed some black marks on his body and one on his head. Then he started to bloat and have problems swimming. I thought this was swim bladder so  tried the pea trick which appeared to help briefly

Now though he has stopped eating and is even more swollen and is swimming into the side of the aquarium really hard. I  visited an aquatic shop and they gave me some protozin.

I am on day 2 of the treatment but he is still really bad. He is starting to "pine cone". I fear the worst. He is either swimming around crashing into the side of the tank or lay on his side/back breathing heavily.

Help Please ! I'm desperate.

I feel terrible. Is there anything i can do?  I am doing 25% water changes every day (i have been for about 5 days now) as i know the nitrate and nitrite level is too high.

Aquarium size: 160 litres

Filtered using an external DIY trickle  filter. The filter has layers of 3 foam types, Kaldnes K1, alfagrog and carbon (the carbon was removed as per instructions on the protozin bottle.

3 airstones

Temperature usually 20 (celcius) 68 (farenheit). I have now raised the temperature in the tank as i understand parasites dislike this.

Ammonia 0
Nitrate 50
Nitrite 0,5 (Not seen nitrite before tonight)
GH  >21 (I was told bogwood would lower this, which i have now added)
KH  12.5 (darker than 10 but not as dark as 15)
PH 7.8
CL 0

Answer
I don't believe it is a burn although you shouldn't have a heater in the tank. Goldfish are fine with room temp water as they are coldwater fish, they can survive freezing temps.

Your nitrate and nitrite is a bit high. Nitrite should be 0 and you Nitrate at least 20-30 PPM. I believe its your trickle filter which can become a HUGE factory if not kept and cleaned properly. I recommend washing the media or replacing some of it.

It is, unfortunately, a late stage of Dropsy. There's not much you can do but attempt to stop feeding it all together or a 2-3 shelled peas a day. Dropsy is caused by severe bloating or even swim-bladder disease. If he's overfed or fed too often this can cause it. Goldfish have a sensitive diet they need little to no protein but a lot of vegetable matter such as diced cucumber, zucchini, summer squash or strips of romane lettuce and shelled peas. Flake's shouldn't be fed too often as its a staple. Goldfish need to be fed 4 days out of a week.

Sorry about the trouble, it sounds like you are taking good care of him.

- Ash