It's been awhile...life has gotten very busy...but I'm happy to report that we're still on an even keel.
25 days ago, we added one emerald green cory and 2 bloodfin tetras to our existing silver-tip tetra, x-ray tetra and neon. Unfortunately, the neon didn't survive. We found it the next day floating at the top, minus his eyes.
During these 25 days, we have only done a 50% water change once in order to clean the algae and a 30% water change once as DS thought maybe the ammonia level was going up (the color did look slightly greenish). The readings continue to be good and the algae seems under control.
So...the current plan is to add another emerald green cory, another silver-tip tetra and another x-ray tetra. That will be a total of 8 fish, 2 of each. If all goes well, DS wishes to add 2 glo-fish. I think that will "complete" our tank.
The tank is still existing with only the underground filter. I've learned that it takes days...even a week or two...for the filtering to take place. I try to be patient as I known DH will not agree to any other filter...yet! Perhaps one day but not yet!
With all that said, I just want to thank each and every one who responded in this thread again. Although you may have answered my questions many times in other threads, you took the time to answer in this thread--the one I was reading and watching. Thank you. You all helped me tremendously and I do feel confident in taking care of this tank.