Our roof was getting cleaned of lichen so that it can get repainted, and we were meant to disconnect all the down pipes, but managed to miss one of them, and now the water in one of the tanks is contaminated with what ever chemical was used, not sure what it is at the moment. Apparently one of our tanks should be fine as the water did not run into it, so I will use that and see for now. Still not going to be fun carrying buckets of water from the bottom of the garden to my tanks to do water changes, but what must be done will get done.