I haven't heard of someone dosing phosguard in years. Really don't understand why you would use it or what you are trying to accomplish.
If you really want some help, you should post as many details and pictures that you can about the tank.
My initial guess is that your problems have little to do with GH & KH, and you probably need more ferts not less.
But again, no one can help you without a lot more information.
I'll test my tank water and tap water tomorrow night. I did my weekly ~50% water change tonight and want it to settle down for a day. Tomorrow is a fert day also so I'll be dosing Thrive+ in the AM before I'm off to work.
I'll also try to gather as much info as I can and put something better together. In regards to the Phosguard, I had previously great success removing brown diatoms with it. I guess I'm a little gun-shy about seeing any brown-ness and thought I'd try to get a head of it. Likely over reacting. I didn't think my test result of about 2.5-3 was "good." I knew it's not supposed to be 0 but wasn't sure on the level it should be. Again, knowing my experience with high phosphate and brown diatoms at one point, I was quick to act in thinking it needed to be reduced.
In regards to adding more ferts, I mentioned earlier that I see a decent algae bloom the evening after dosing in the AM. I would imagine adding more would be bad, and likely you're response will be that I need to ditch the Thrive+ all-in-one bottle solution and start doing ferts for real.
I imagine I've got an imbalance of ferts I need to sort out. I just don't want to be swimming in test kits.
As for CO2 ppm, I go by the drop checker in my tank and know that full yellow should be pretty
saturated. It's typically that way by the end of the day.