I know people who use Prime to cut down on ammonia spikes (fish that may have died and they didn't catch and so forth). Of course, its only a short term solution.
Also remember that Excel requires the light on after dosing.
Using Prime, adding an airstone/powerhead to introduce O2 through agitation and water changes are good temporary measures. That should knock out the cloud.
I haven't used Excel too much but is there a reason for the first dose being heavy?