Tank fogging up

Question
Hello. I've recently purchased a 5 gallon acrylic tank for my betta. I have not put my fish in it yet because I want to test out the 25 watt heater I have in it to make sure it's the right temperature. I have had the heater in for about a day now, and I've noticed the top part of the tank walls (where there is no water) is fogging up. I think it's water vapor because it's only on the walls. The rest of the tank where there is water is fine and clear. I opened all the hatches and holes on the tank hood, and it's not fogged up directly under the open areas, but still on the sides where there is no ventilation. Is this normal? I'm worried it will deprive my fish of oxygen since betta need to breathe from the top. Have you ever heard of this problem and is there a way to stop it from happening other than keeping the hood up?

Thank you.

Answer
Chris, Because you took him out of a bowl and put him In a tank it is going through a normal tank change. What is going onis a bacterial bloom. Just curious did have you always had a heater in with him? It really isn't necessary and usually for small tanks like that unless you a maintaining a temp lower than 74 your fine unless they are having a problem eating. Though the sweet spot is 78 to 80. When you put a new tank together and it is aquarium and not a bowl it goes through all the things a tank does. What you are having is what they call a bacterial bloom as I said...which is the bacteria growing it will eventually settle and it settles into the rocks. The reason for this is it is cycling out your ammonia will go up till the bacteria settles than that will eat the wastes and recycle them into nitrite...then again into nitrates. If you are going to keep him same way as usual water changes and cleaning everything don't worry about all this. Everytime you have a tank cleaning this will happen for a couple days.Do not overfill and they will breathe from their labyrinth organ and be fine. Good Luck, Tina