welcome to fishlore!!!!!! sorry about all your fishies being sick

sometimes thats the frustrating part about keeping fish.....
first a few questions....what
test kit do you have? what are your water parimeters at this stage ?
if its ich, and you can see it, its already in the 20 gal by this point and turning up the temps to 83 for two weeks, some extra airation for warmer water has less oxygen, and some 2 gravel vacss a week to get the ich spores out of the gravel, will help the ich....
if you arent cycled by whatever your water parimeters are, thats another issue that we can help with once we know your readings....
do the white lines look like lil worms? google planaria as thats probably what they are and are harmless and your fishies will eat them most of the time...but also, water changes will get rid of them as welll..so get your readings and go from there and I hope things look up soon!