Hello again.
Have done a bottom clean, lots of shit & waste in the water, plus gave it a good clean out.
Have both tubs going through a filter now plus have added some Pond-Zyme Plus pond cleaner, i use this in my big ponds to clear up unwanted waste, very good stuff.
I will keep an eye on things over the next week, see what happens.
I will continue to use the Malefix, cant see it doing any harm.
If you have any more thoughts on this please advise.
Thanks again for your help.
Cheers the SHARK