Civic Chick (I also drive a Honda Civic...I usually love that car, but the air just broke on it and it's 100 degrees outside
) - I'm sorry for the tone that was used, a tone like that is no way to educate someone.
When you're "topping off" water, you're not doing any water changes, because what's evaporating out is pure water. All of the wastes stay in the tank, and in fact get more concentrated over time, as the pure H2O evaporates. In order to actually improve water quality, you need to change water weekly - not just add water back that has evaporated. In a tank as small as a 5 gallon, your best bet is to take a container like a big yogurt container, and just scoop out the water into a bucket. You have to change about 2 gallons a week.
A Chinese algae eater really has no place in a 5 gallon tank - check out how big they get! 200-280 mm = 7.87 inches to 11 inches.
http://www.seriouslyfish.com/species/gyrinocheilus-aymonieri/
I'm not sure who told you they don't count - of course they do
They eat food and produce waste, and as you can see they'll get much larger than your puffers. I hope you haven't been told that "fish only grow to the size of their tank" business either, because that's completely not true...
If you need an algae eater, olive nerites are probably the only ones that fit in a tank this size. I don't know how they would work out with puffers. They're pretty big so the puffers may not try to eat them, but you'd have to research this further if you're interested - I don't keep DPs, but I do have olive nerites and none of my aggressive fish have bothered them, from convicts to red tailed sharks.
I would put the guppies in Craigslist or your other local classifieds...people are always looking for free fish!