Yes, do not paint any fittings period, the paint chemicals will eat away at the finish, and if plastic they can break down the plastic as some of the chemicals are absorbed into the pores of the plastic before curing. Many fittings are known to pit if painted with antifouling paint. These fittings have a coating to protect them and should not hold growth, if they do, it is typically because the boat sits for extended periods of time, I'm talking over a month with no use, usually it will wipe off with a simple rag as long as the groth is wet, but it is unlikely to have groth on them if they are not pitting or breaking down. As for hoses, no growth inside them, the algae needs sunlight to live and will not grow inside where it is dark so no problems there.
