sick neon update and filter question

[russjet]

down to five neons :sad i thought they were doing great and then one just peeled away from the school and just died in front of me
but it seems to be the less spotty fish that are dying
maybe just weaker neons but i feel awful

question on the filter is i have a fluval 4plus
i have seen a spray bar attachment but it didnt say what it actually does
does it go above or below waterline
i am currently using the filter with the venturi valve above water and the output below to inject bubbles but i wonder if the spraybar may be a better alternative ? would it stop the current being quite so strong and also i would then not have so many airbubbles roaming round the tank

another question is how long after i eliminate the white spot do i not introduce new fish? (will need to make up the schools number to keep the neons happy) i dont want new fish to get ill too

if they all die i think i will do a fishless cycle
unless i can find some biospira in the uk
then i might be brave and try it
anybody know how to get it in uk?
if not i want some biospira to improve the water for the neons that survive