hi there, from my experience you might be best to buy a master water testing kit from your local aquatics shop & test your water parameters (ph level, ammonia, nitrite & nitrate levels) especially if you have fish dying. if its misty water tryin putting some carbon in your filter (like a black gravel box/bag of stuff), this is also easy to get for about £4 from your aquatics shop. this makes your water crystal clear but shud need changing after about 3 months. This may also get rid of your algae. I hope this helps....