Swamp Cooler help

Sounds like I should use a swamp cooler. I have always been hesitant to try. It seems like putting the carboy in ice water will make it too cold.
Questions:
-Can I still rely on the thermometer stuck on the side of the carboy for the wort temp assuming it is above the level of the ice water?
-How long do I need to keep the swamp cooler going for? I plan to use Safale-04 in a porter, it sounds like it will ferment fast with this yeast. I assume I can stop adding ice once the real active fermantion slows down?

Expect to use it for at least a week. Once fermentation is almost finished the warmer temps will have less of an effect. I usually put about 4 frozen 1L bottles in twice a day to keep temps down.

I use a thermometer clipped on the outside of the swamp cooler that goes into the water to give me a temp of the water. The temperature within your carboy shouldn't vary so much from the water outside of it. Not exact as some other setups but works great for keeping fermenting temps in check close enough for me.

I usually just keep the swamp cooler going through the whole fermantation. I guess I just think why not, to be on the safer side. But that's just me. A week, week and a half will do just fine.

I also keep the swamp cooler going throughout the entire duration of fermention. The first 3 or 4 days are really the only time you need to keep a watchful eye on it. After that, the water just insulates the carboy and keeps temperatures consistant.

I use the thermometer on the side of my carboy to guage the temperature. I also leave a floating thermometer in the water on the outside. I think this setup helps me figure out how much the temperature will drop when I add another ice bottle. The water generally cools to about 3 or 4 degrees below the carboy temp when I add an ice bottle, then slowly warms up to the wort temperature over time. Once the two have been even for a little while, I know it's time to add another bottle before the temperature in the carboy begins to change.

I think it's a safe bet to use the thermometer on the carboy (as long as it isn't submerged in the water,) especially during the first few days of fermentation because the yeast will constantly stir the wort as they move around. This should result in a nearly uniform temperature througout the carboy.