Tank temp not stable

[BaraBlu]

Hey everyone, I'm a newer reefer and I've been having some trouble keeping my tank temp between 76-80 fahrenheit recently. I keep it in my sump in the camper after my filter sock. Sometimes the temp likes to dip down to 75 and just want to know if I'm doing something wrong or any advice. My tank is a 15 gal cube with a 50w heater as usual. I can assume my ac vent facing it could be the reason as to why so I recently changed it's direction of flow away from the tank. Besides that when I set my heater to 78-79f it never likes to stay there and prefers to be colder. I also only have the tank return pump as flow ATM which could also be a reason why it's not constant but wanted some opinions if I'm wrong or correct. Besides that I appreciate anyone who reads this paragraph lol, I just want everything to go right with my tank

 

[DED65]

I don’t think that a temperature drop like that will cause any issues. If you are worried, you might think about going with a 75 watt heater.

 

[Townes_Van_Camp]

I would also recommend in addition to the 75 watt heater, running it through a inkbird itc 308 aquarium model (it has a black plastic temperature probe).

Not only will it protect your tank from a failure that is certain to occur. It will regulate and stabilize your temperature within 1° f +/-

It also has a plug to add a fan. It will turn on the fan if the tank gets too hot.

Here is a link:
Inkbird ITC-308S Aquarium Heating and Cooling Dual Stage Temperature Controller
https://a.co/d/85mGwds

 

[Mr. Mojo Rising]

Your heater is a little small at 50 watts. Using the 3-5 watts per gallon rule (I always use 5 watts), so 5 watts x 15 gallons should be 75 watts. I might even go for the 100 watts.