Temperature Fluctuations in Bowl - Should I get a heater?

[shrimpy4]

In my new office, my 1-gallon bowl sits right by my window and when I come in in the morning the shrimp seem super happy with the warm sun shining in. They're at their most red, and wander around liberally but not frantically. My (now two) hermit crabs are also very active, as are the snails. I think the Chaeto is also finally starting to grow now that it's seeing direct sunlight.

In the afternoon after the sun has moved away, I think the temperature of the bowl starts to drop rapidly in our air conditioned office. For a few hours the shrimp do more of a round-robin circling around the outside of the bowl, the hermits and snails pretty much just hide out in their shells, and condensation forms on the saran wrap I use to cover the top of the bowl (I have holes cut in it so there's still airflow). I checked the temp and by about 4 PM it sits at around 74-76 degrees, and the shrimp stop their swimming and the hermits also start wandering again.

I know that's still within the ideal temp range for the shrimp at least, but for the overall bowl should I invest in one of those disc heaters that won't let the temperature drop below 78 so the heating is more consistent? It's too late for me to actually put it into the bowl, so I would just sit the bowl on top of it. Not sure if it would even make a difference heating from outside of the bowl and under all the substrate.

[Mustafa]

74 degrees should not be a problem at all for these shrimp. Plus, the shrimp being "active" does not necessarily mean they are doing better. It can (and often is) a stress reaction if shrimp swim around a lot. Plus, I'd be careful about the sun hitting the little bowl as it may overheat it, especially in the summer. If it's just an hour or so, it should be fine but several hours can be a problem. I'd keep an eye on the temps in the bowl.