Sorry about your loss, here are my thoughts:
1. That tank is way too small for even 1 clownfish, much less 2. Maybe a shrimp/goby combo would be pushing it. If you want to keep a couple of clownfish, you should probably upgrade to 20g minimum. They'll likely kill most anything else, I have 2 clownfish in a 29g, and they bite me and attack anything that gets put in.
2. Next, get a timer for your lights. You can get one at walmart for a few dollars. Looks something like this:
Then your lights will go off and on the same time everyday, and it's cheap. I still use these on my 3g paludarium.
3. Throw that PH stuff in the trash. Increase surface agitation or find a way to increase gas/oxygen exchange to raise your PH. Even then, any number between 7.8 and 8.5 is acceptable, what's most important is it's stability. It'll change slowly over the day, and that is normal. There is no reason to take any action unless it is out of that range, which likely won't happen, and if it does - increase oxygen rate.
4. Throw away the purple up. It's just a calcium supplement and you aren't using any of it. Maybe one day in the future you'll start getting coraline and want to keep it. But on something that small, water changes are fine, and for any other purpose purple up is a terrible choice - it's mostly water. You are probably overdosing calcium, which isn't going to kill things, but it's not ideal either.
5. Keep your hands out of the tank. Meaning - stop doing so much. Kind of goes in hand with the above, but also all the other stuff you did.
Good luck. All you can do is learn from the mistakes.