(talking about my 10 gallon planted aquarium, no soil just gravel, HOB filter)

so I recently added the yeast co2 generator thing. it's very low tech. a gatoraid bottle with a tube coming out of the cap and inserted into the aquarium. I squeezed a sliver of sponge in the tube to act as an air stone. it works well so far. I had that going for a few days and then decided to change my yeast sugar mixture a little and try again. shortly after putting it back in the tank the bubbles were coming out pretty fast and a few hours later my chinese algae eater was swimming weird. he started acting like a dying fish and laying on his side or upside down. then he would shoot up and try to swim around but lost his strength and sank to the bottom agian. I checked my PH level and it was about 6.0 (very yellow!) it was at about 6.2-6.4 a few days before after a water change. usually the PH from my tap is pretty high closer to 7.6 so when I decided to test the PH after a water change I was surprised but thought I would wait a few days and test again. anyways, when the algae eater was looking very sick i tested the water and it was very yellow/orange after adding the test drops. I got online and read about too much CO2 lowering the PH so I started adding oxygen by pumping bubbles in the water and lifting up the HOB filter to create turbulence. long story short the algae eater died. the thing that has me confused is that the internet says that the chinese algae eater is a pretty hardy fish and can tolerate a wide range of water conditions. I also have about 10 little guppies and a 1 inch pleco. the pleco was going to the surface for gulps of air for a while and I know that is a sign of poor water conditions, but the guppies I have are tiny an I would think that poor water quality would affect them before the algae eater that is 3 times their size, especially since (from what I have read) guppies are more picky about water conditions then the algae eater. no other fish showed any signs of stress at all and the tank seems very healthy now (and then)...

was the algae eater just having a shitty day or what? did I add to much co2?