I would say you do need bottom paint if you plan to be in the slip for a few months or more. Try a search here for bottom paint fresh water and some threads will likely turn up. If you want to do a thorough job, you should also put a barrier coat on the hull before the bottom paint. Try a search for that also, likely plenty of threads. Ive been using Petitt Vivid bottom paint and its worked fine (just pulled the boat out of a fresh water lake after 5 months). One caution.. do a good job picking the bottom paint because the different paints may not be compatible meaning if you decide to change, you may have to completely remove the old paint (UGH - horrible job).
I dont get a smell from the ballast tank in the lake where Im at but I understand some do and just add some Clorox to the water if you do have an issue.
My previous owner kept this boat in a fresh water slip and I have been doing that for four months a year for the last three years. The water ballast really doesn't present much of a problem - at least so far (the boat is ONLY 28 years old now.).
