Hi, thanks for your reply. If all you are feeding the frogs are the pellets which my frogs hate, and frozen bloodworms, I would consider offering a few more stinky frozen goodies. Most will say that the bloodworms are low in nutrition, and though the frogs love them they should really be considered more as a treat and not fed too-too often.
A variety of stuff is good to help make sure they're getting enough nutrients that they may need. Some easy to find pet store foods are: frozen brine shrimp, frozen mysis shrimp, frozen krill. Brine shrimp is terribly messy and will go all over the place, mysis shrimp is a lot cleaner and won't break apart, frozen krill can be little chewy and rubbery so if you try that be sure to offer tiny pieces (it's basically small shrimp).
I've heard the same "treat" information regarding frozen beef heart, most of the above are offered in the same frozen style cubes as the bloodworms, some in small baggies.
And yes, good idea about allowing airflow to reach the inside. Since the frogs do surface to breath it's good to have a nice flow of fresh oxygen reaching their air and water.
When changing the water it's been suggested to make sure the frog's current water and the new water are the same temperature to avoid any sudden changes in temp. or shock, just like when you are in a warm shower then things suddenly turn ice cold! If you don't currently have a thermometer inside, good to have one just to be sure the temps are within the 72 - 80 range, yes 75 is what a lot of places recommend.
Have you read about "cycling"? Possibly since you're not doing full water changes, I have info from the The Aquarium Wiki which I can't post because my post count is still too low, but I will PM them. Very helpful info for newbies.
And unless you have a filter in place and you're testing your water to be sure that all the dangerous levels are in control, you may want to consider doing water changes more often. Maybe about 20% every day or every other day and save the 50% for once a week. I too only use about 2.5 gallons and myself and others with similar set-ups are usually suggested to change the water more often since we are using less water that can dirty up a lot quicker. The comparison I've read which I can't seem to find is something similar to dropping one drop of food coloring in a bathtub filled with water. Takes awhile for it to reach other places or even be noticed, but drop that same single drop in a small glass and it's very noticeable and doesn't take long for it to spread. Waste and harmful elements would replace the drop of food coloring. If you don't already know, many pet stores and aquarium places should offer to test your water for free, my Petco does. A small container for a sample should be fine - even something like a pill bottle would work, just rinse it with treated conditioned water if you think there's residue inside which may affect test results.
There's tons of info online and lots to learn about the frogs and their care which is why Brookstone and Hallmark should not sell them because the care info they provide it so off and completely wrong. I think you should consider looking into all the info I have PM'd you especially if you still feel new and unsure about lots of things, and are still learning as you go along as I am. Lots of helpful things, questions, and answers on there.