redcap and fantail sick

Question
hello there miss Tina, i got a redcap and a fantail that are sick with streaks and ich im giving medications like quick cure for ich and adding aquarium salt and antibiotic but the streaks are increasing badly their tails are already wearing off this has been for about 5 days now....
now my redcap and fantail have like a gluey coat and they feel so slippery am i right with the diagnose or is it velvet ???
i have them in an 18 liters home they have been there for a year happy and eating but they were infected by a bubble molly that i newly bought... Is there a chance they survive?? i love my fish i dont want them to die but my redcap totally lost apatite now for 3 days didnt eat she has clamping fins too and lethargic..
is there anything more i can do? i also do daily water changes about 50% of water.
thx in advance

Answer
Angy,    When you clean your tank you are using a syphon and cleaning them rocks of debris and (poop). This is a tube with a hose that creates a suction and drains into a bucket. Then your water change. Never shake up you rocks to clean like that it will kick up the bacteria living  in your tank and stick to your fishes slimecoat and eat it. Even though ick is considered parasitic sometimes actually there is no perfect answer for ick just many arguments. What I think you need to do is syphon one more time go and get tetracycline for your tank the streaks are an indication of a bacterial infection and water quality problems. SO go get your syphon and tetracycline do a 30% change. Take you carbon out of your filter so it doesn't take the medication out of your water but keep filter running to keep oxygen in your water. Follow the amounts for your size tank and it wouldn't hurt to get some stress coat and try to get it over the fish with the coat drooping. Keep you goldfish with goldfish don't mix with tropicals. If you want to put an algae eater in there fine go with a plecostomus or pleco. When tank is back to normal. Tanks can be balanced for a long time without the correct way of cleaning and then crash just like that. After your medicating do a 40 to 50 % water change and clean every 3 weeks to a month with a syphon (so important). You should be fine. If you have a heater in there take it out. While you are at the pet shop get one of the suction cup clips and give them at least once a week a slice orange thin slice pulp out maybe two slices depending on how well they eat it. They will love you for it and it keeps them from getting vitamin C deficiency. You have anymore problems get back to me ......Good Luck , Tina