For PH, I do my best to keep it as close to a 7 as possible. Mind you if its a 7.2 i'm not going to add anything as I've been trying to make the minimum amount of changes to help the tank "do its thing" as its still in the early stages of cycling.
For temperature, I have my Betta which prefers high 70's, low 80's so I tend to meet on the middle to high on this. Around 78 to 79 degrees.
As far as filtration, I am currently using a Medium sized aquarium co-op sponge filter. I have my male Betta in this tank so my original HOB filter just had to much flow to keep it on this tank. I have a Marineland Penguin 150 coming on Wednesday that I plan to throw on here to help with the mechanical filtration as recommended by someone on a different topic of this forum. Might have to modify it a bit to help keep that flow from being to strong for my Betta's fins though. Waiting to test it first.
You are 100% right on the advice. I haven't had time to respond but I have read word for word every single reply on this thread and I can't express my gratitude enough for everyone's advice and stories. While I'm here to find some answers for myself, I truly hope these comments and advice will also help the next person.
I couldn't help but chuckle at this but at the same time, your 100% right. (About the efficiency) Looking back, it was a bad move to do both at the same time and I obviously regret it now. It absolutly could have been the difference in temperature or PH of the water coming back into the tank. I'll have to keep a closer eye on that going forward or do my best to match them appropiately.
As far as water conditioner, I use this: https://www.petco.com/shop/en/petcostore/product/imagitarium-betta-water-conditioner
I've asked Petco the last time I was there if there was anything "specific" that made the water conditioner different for Bettas. They gave me the typical saleperson answer. "Well if it has Betta listed on it then it must be special"
I can't say I agree or disagree (With above Petco salesperson statement), but I am probably going to switch to something more popular like Fritz going forward. Again, not to say it was or wasn't the declorinator. It might have been working fine or maybe it needed more time to bind up the Chlorine and Chloramine. Can't say for sure.
As everyone has mentioned, I am going to look for other signs of stress, and take a step back and look at the bigger picture for posible stressors and do my diligance to reduce them before making drastic changes such as major water changes.