I have been running 5 antminer u1's for 2 or 3 weeks now and I have a USB fan to cool them. When I started using them I noticed based on the site for the pool I was getting about 7 to 8 Mhash/s. Now I'm getting just over 6. Is this due to difficulty going up or do I have a miner about to fail?
if you are only getting 7 or 8 MH there is something really wrong. you should getting GH
And if Gh, then yes - it would seem one (or all) are not up to par. I am not sure what software you are using for that, but if possible could you run them individually? If you could , and then could set each one up for a mining instance then you could compare them to each other.