Hi,

I am now trying with a little less sand in, will see how it goes.

Regarding new sand and your problem I suspect that the ols sand had
become worn and lost its sharp edges enabling it to sit closer
together therby trapping everything passing through. New sand will be
sharper and thus leave bigger gaps. I would suggest adding more sand
but that may lead to the same problem I have. It should improve for
you once the sand has worn a little.

Carl