If you can, try to pick up a better test for nitrate like Salifert as the API test kit is notorious for being inaccurate at the low-range. For example, salifert can go as low as .2 ppm which can be very helpful in this situation assuming you are a color expert

. You can keep running carbon but run lower than the recommended amount. Purigen+Chemipure+carbon may be stripping the water a bit too much but the phosphate reading seems ok. Nitrates you would want 1-2ppm and alkalinity you will want around 8, calcium a little higher in the 420-440 range. I think magnesium you will also want 1300+. My torches don't necessarily like alk below 7.5 so I try to maintain mine right around 8.
PH at 8 isn't necessarily a problem but if you can get it to 8.3ish you may have better success. Any idea what the parameters were on the tank you got it from? They can take a week or so to adjust depending on how big the swing in parameters are.