back dust turns slimey

[steve]

me again, carrying on from my previous message. bought myself a water testing kit and everything seems to be fine, the ph reading shows ph9 and there is next to no trace of nitrate, nitrite, or ammonia. the black spots my yellow labs had are now brown slime, am i right in thinking this is velvit disease? or am i just panicking over nothing. all other fish seem unaffected.