Hello! I have an old HOB heater which cane with my current 55 gallon tank (got it off Craigslist) and I've tested it and it works so now I'm using it on my goldfish tank to maintain a good temperature but I'm just not sure if it is reliable, I'm worried about a malfunction. I haven't seen any signs of failure it just looks old so I'm not sure. The brand is Penn plax and it's one if those glass ones which hang out of the water and dip into the tank where it heats the water. If this heater should be retired, what brand would you recommend that is relatively economical, but still efficient and most importantly trustworthy! Thanks!