Good for you for trying to take care of your parents' fish. They're certainly better off in the 3 gal tank than in a vase, but--as I bet you've found out online--common plecos get HUGE! :eek3:
Your pleco can grow over 18 inches long. He'll be a big, fat fish at that point--and they grow fairly quickly. Unfortunately, he won't survive long in your 3 gallon. And it sounds like a bigger tank is going to be way over-priced for you. If you don't have any friends with a bigger tank who could adopt him, maybe consider giving him to a pet store.
You may not get any money for him or anything, but the pet store would probably take him. I'm in Hawaii, and like Guam, we have to worry about invasive species. People dumping aquarium fish in streams around here is a big problem. So, pet store are required by law to accept fish that people bring in. I bet it's the same in Guam.
Do you know anyone who has a pond? Your pleco would do just fine in the outdoors.
Anyway, I was able to find a 3 gal. bowl, which the fish are in now. I change out 1/2 gal. of the water every other day, and do a full water change every weekend. There are plenty of live plants in the water in order to make sure that there is oxygen supply. Also, i use a chlorine and chloramine neutralizer and an ammonia "extinguisher". I do not test the temp. of the water. I do not worry too much about that because Guam is a tropical island with tropical and warm weather. room temp water here is never too cold and never too hot. if i had to guess the water temp is probably high 70s to low 80s.(just a guess)
Your water change schedule is very good--but plecos are very messy fish--don't hesitate to change some water every day.
As for temp, I think you're ok. Here in Hawaii, I don't use heaters either.
since they got the pleco, i have been trying to feed it cucumbers, spinach, zucchini, lettuce, peas, and algae wafers. he took to the cucumbers and zuchini before, but he would just suck on them. Not sure if he really ate any of it. However, he loves the algae wafers, but its still not satisfying cause i know they are supposed to eat lot of fresh veggies.
It's ok for now if he's just eating wafers. In such a small tank, it's easy for the water to get polluted from food, so make sure you don't leave wafers or veggies in there if he's not eating them. If he doesn't finish his wafer, take the rest of it out.
Also, I have been reading about people euthanizing their fish. If this is the best thing I can do for him pls let me know. Although it hurts me to even think of having to do that to him. I really love this pleco and I want him to live happily. However, I would raher not have him live if he is living in pain.
I say, euthanasia should be an extreme last resort. If he's got dropsy, he may be too far gone anyway. Can you get a photo of him and post it here?
If you can get him back in good health, then it's better to return him to the pet store than euthanize him.
And, I don't want to sound morbid here, but if he were to pass away from dropsy, then your 3 gallon tank would actually be ok for the betta. Is it a tank or a bowl? Post a picture of that, too, if you can.
Anyway, you're doing the right thing by doing lots of water changes, and by researching your fish's needs online. Good luck with him!