Hi Nigel, Thanks for the quick reply. we did suspect that it could be mosquito larvae but had read that they don't like chlorine. is it ok to use antialgus without having a pump or a filter? we had a look at some in sabeco but it said that it could only be used with a filter.
we will clean out the balsa once all the water is used but its a lot of water to try to use up and quite expensive to replace. unfortunately we are rather skint after buying the finca.
thanks again for the advice you have saved us hours of trying to find a solution on the internet x