Unexplained Blue Water (Not The Shopping Centre)

[Martinspuddle]

two plastic plants, a barrel, an anchor and a fake bit of coral

Remove these, see what happens.

[Roy's Mum]

Hi all, just a quick update. It seems to be gradually lessening as I'm gradually swapping out the sponges for new ones that aren't blue, so I guess it was the sponges. It's the sort of thing that happens with clothes only the other way around - the colour comes out when they're new, not when they're old! Thanks so much for all the advice.

[YnotFish]

Thanks for the update, the suspense was killing me!