A pleco is really too large for your tank. They grow to be over a foot long. He is probably okay for a little while, but they are large waste producers and as they grow they stop eating algae and just eat anything and everything.
I would seriously invest in an API liquid test kit so you can test your own water. That is really the only way to control the water parameters in your tank. I really on mine very heavily. I am cycling a 100 gallon tank now and I test the water 2x a day and make one or more water changes a day (I have some prized fish in the tank).
I agree that the cloudiness is bacterial bloom. Don't add any bacterial supplements, it is a waste of money. And water clarifiers make the water conditions worse in the long run. The less you can add to the water the better (unless you are talking about Prime or Tetra Safe Start). If you can get ahold of a bottle of PRIME that would also be awesome as it detoxifies the water of ammonia and nitrite for 24 hours until your next water change. But, it does not REMOVE the ammonia and nitrite so your tank continues to cycle. The stuff is a miracle worker.
