50 Gallon Tank Urgent! Goldfish at the bottom of the tank laying sideways

My ryukin goldfish is living with three other ryukins and yesterday it was at the bottom of the tank barely moving. Today it is now laying sideways and still at the bottom of the tank. He did have swim bladder problems at one point and feeding him Repashy stopped him from floating up. I am far from home (college) and my sister lost the tube needed to collect the water and test for the water parameters. Ordering online will take about a week and I won't be home until next week, not sure if he will survive by then.
He is now in a quarantine tank with a heater but I'm not sure what to do next. He does not seem to have dropsy and I've had all of my goldfish for over a year now.

 

Swim bladder can cause being stuck at the tank bottom! A shallow clean qt tank, and a pea diet, should help

 

Swim bladder can cause being stuck at the tank bottom! A shallow clean qt tank, and a pea diet, should help

How often should I clean the quarantine tank. Should I fast him for 2 days and then feed him peas? Thanks for the reply

 

How often should I clean the quarantine tank. Should I fast him for 2 days and then feed him peas? Thanks for the reply

Yeah, first fast for 2 days, then feed peas! How big is the qt tank?

 

The tank is 10g. What I'm mainly concerned with is why he is on the bottom of the tank. In the past, he would float upwards and if I feed him a little less than the other goldfish, he will be able to swim properly.

Yeah, first fast for 2 days, then feed peas! How big is the qt tank?