I have a baffled fibreglass water tank where I can get into only one of the areas. There is a round lid about 180mm diameter. The floor and walls of the tank that I can see have a covering of slime. I've rubbed it with a stick and it comes off, so that part can be cleaned with a brush. Does anyone have knowledge on how the baffled parts that I can't get to be cleaned? I suspect there is no way but thought I'd ask just in case. I do plan to install a filter but it would be nice to have a clean tank!
thanks in advance

Silas,
sounds like they cant be removed. A good dose of bleach, let them sit full for a couple of days, drain, flush, keep doing it till your happy with the taste, smell ect.

I got my tanks out, got them home, cut an access hole in them, aluminium. They had what looked like small white rocks inside which I have been told was calcium. They stunk, couldnt believe I was drinking out of them, did as above. Every now and then when I fill them I drop one
Miton tablet in, haven't noticed any bleach taste yet and all seems good

Good luck, Mike

If the slime is brown it's mostly sediment from water supply and harmless. It's the same as what is in all water tanks in buildings around the city or and break tank (like toilet cistern). I'm a licensed plumber of 30+ years so seen it many times. If you're really concerned just instal a filtration system. I have the same in mine and never bother removing as it just takes ages for the brown to disperse once disrupted.

Thanks guys,
no, I can't get the tanks out. The boat has an integrated keel and the tanks go down into it, then the cabin sole is over the top with small access hatches which pull up to reveal the round tank inspection points.
think I'll just do the filtration and never open the water hatches!

Add some of this for long-lasting protection against harmful beasties and goo in your tank.
www.daveywater.com/au/product/acquasafe-liquid-disinfectant-for-tank-water
At a 1/2 capfull per tank, the container lasts a very long time. I've been using it for years, and as saltiest1 says, brown slime won't hurt you.

Bleach is good, but the it doesn't last long as the chlorine evaporates out of the water.

Also fit a 1 micron carbon filter. The 1 micron will remove giardia and the carbon will remove the chlorine taste if you dose with Milton tablets or the like. Replace the filter every year. Downside - the 1 micro probably needs electric pump assist.

Thanks Wangaga and MC, I've bought a .5 filter that will remove everything harmful. I have an electric pump also