I wish to remove the perspex top of our water tank, clean the tank with bicarbonate of soda, and refit and reseal the perspex top. Has anyone experience of doing this? Is it tricky to remove the top, and is there a risk of breaking the perspex? And what product is recommended for resealing the top?

Arbosil 1081 black or clear to choice.Basically aquarium sealant /adhesive used for making tanks.
It's what is used to fine point replacement hatch perspex perimeter after bedding on butyl strip.
I used it to rebed my cabin windows successfully after several attampts by others using neoprene tape.
Available Hadlow Marine /Construction Sealants etc. , about £8 per tube,plus any postage.
I assume there's a wide perimeter bed so the sealant is going to be more convenient than a narow butyl strip but thats an alternative.

Hi,
I took off the perspex top of my water tank over the winter as there was discolouration of an arc of the marine ply, presumably from water getting between the ply and the perspex. Also took the chance to remove the little black "floaters" that seem to have accumulated in the bottom of the tank and let it dry out completely. There did not seem to be obvious sealant as such between ply and perspex, so I just re-varnished and screwed back on the perspex. Having now seen Peter's reply, I may have to revisit the job to prevent prevent further water staining.
Did you try the sealant suggested?
Bob S