Hello everyone, we've had my tank for almost 5 months. We recently had a huge algae and diatom bloom. I decided to do a 100% waterrible change since the pebbles were brown (originally rainbow colored). I allowed the tank to run without our fish for a while and then safely transferred them (I used to do this with my dad when I was younger and all of our fish were fine). For some reason our guppy started acting weird and is swimming almost vertically. He eventually drifts and stays vertical for a bit. I checked the water parameters and they are as follows: pH: 6.4 Amonia: 0 Nitrite: 0 Nitrate: 0 I ran the test twice ( I have the API Master Test Kit) and still got the same numbers. We are extremely worried about our guppy. We've considered adding baking soda to help the pH but are scared to do so. We think that it might be a pH shock? Or maybe constipation? Swim bladder? Not too sure and multiple forums have given us mixed information. We really appreciate your help and advice. ~Worried fish parents.