Is there no filter for your tank?
If not then you will want to be doing 1 50% water change per week, with 1 100% monthly.
If there is a filter, then just 1 25-40% water change per week with regular siphoning/vacuuming of the gravel.
Is this the Stability
you are adding in? As that could very much be the cause.. the only chemical you should add when doing water changes is just a regular water conditioner. I am assuming you have no filter since you did not mention it, and that you have done a 100% already in it.
Stability is more for a larger aquarium with a filter.. and even then it's not needed when cycling a tank. (If yours has no filter, you will not establish a true cycle.) Basically you are playing with the chemistry when no playing is needed :) so taking that out will most likely stop the clouding up.
For now I would go ahead and do some smaller water changes- do a 50% and add in only the water conditioner, and not Stability- then in another day or so do another water change and see how that goes. Just remove the water, adding in like-temp water and conditioner.
If after 2 of those water changes and still no change, hate to say it but do a 100%, rinse the gravel out very well in hot water, fill it all back up and add in only the water conditioner. That should work- is there a lid of sorts on the bowl? Think if there is a way dust or something could get in there easily and could cloud it up- is it uncovered and beneath an air vent? Something along those lines- that is if it doesn't clear up from the water changes.
Also for the heater- if the water is real cold to begin with, a lot of those small preset ones don't get warmer then just a few degrees over the room temp, to make it easier on the heater to stay stable at the correct temp- whenever you do a water change use a thermometer and try to keep the water between 76-78*. That trick usually works for those types of heaters- get the water to the correct temp and they tend to stay there.