That doesnt look like mould on the Ytong, i think its probably just mineral deposits that are coming out because of the water, dont worry about it
Mouldy bits in the basin you should remove, also remeber to remove any food not eaten 24hrs after puttin it in there
In the farm, is it the green and brown splodges that are the mould, hard to tell from the pic, did you cook the sand before puttin it in? always a good idea to put it in the oven @ 200C for half an hour before puttin it in the farm. Looks like you need more ventilation in the farm and less moisture, if you are careful, remove the lid of the farm, get an old t-shirt, and strech a piece of it over the top of the farm and fasten it down very tight with elastic bands, leave it for a few days to a week and it should clear up (make sure theres no gaps for the ants to get out of!)....of course this is only good for species that wont chew thru the t-shirt, what species is it?