Fish And Shrimp Deaths

Hmm you're right that there's an extractor fan more towards the kitchen area of the flat I'm not sure if it's ever been on or not tbh. I think I should test my water again and see if anything odd is going on.  Unfortunately I'm away for nearly two weeks now (the second week my boyfriend can feed the fish though and keep an eye on them).

I have had another thought... The tank is near the balcony which we have open a lot and a lot of building work is going on around us permamently.. We get a lot of dust on window sills and the balcony so this of course could be going into my tank  With winter approaching at least we won't have it open as much but it gets so hot in the flat otherwise (luckily the tank remains quite consistent)

One of the many things I learnt working for a housing association air exchange from extractors lol.  That's good news about your shrimp and I think everyone has had at least 1 dissapearing fish story.  As u say the building work could be to blame especially if they are tearing down old buildings or putting a damp proof course in your building.