How do I make weather loach adjustments to my tropical tank?

I recently started a 30 gallon tropical aquarium. It currently has 2 guppies, two tetras, a placo that only grows to 6 inches, and two black weather loaches. The problem is the weather loaches. They like cold but I never knew that until I looked it up. (They were a gift so I didnt know how to care for them) the temp is 81 degrees constantly but it has to be lower, can I lower the temp without harming the placo guppies and tetras? If so then how much? Also is there anyway to keep them on the smaller side to avoid overstocking this small tank? I had them for a week and they are highly active at night and seem ok, but I want them to be happy. Thanks

you can lower the tank to 78 degrees, but that is it, the weather loches should be fine at 78 and so will the rest of the fish, just do it carefully, so it doesnt get too low, then you will have to adjust again, and this is not great for the fishBut no you can not stop them from growing, and they do get quite big, though they grow very slowly, maybe you can upgrade the tank or find them a new home before then.These are active fish that could acidently hurt other fish when the get bigger.I hope you will get at least 4 more of the same species of tetra, these are schooling fish.