[lcstorc]

If you are afraid of turning out the lights, then reduce the photoperiod. That would be a compromize between the two.
I absolutely agree about the purple up. It will throw your chemistry way out of wack. t messes with not only the calcium but the alk and can cause major problems. Stick with separate supplements as your tests indicate. Increasing your light on the cheato can help some as well. It will grow faster and allow it to remover more nutrients. Remember the root of the problem is excess untrients usually from overfeeding. Re-consider your feeding routine and cut back a bit. Also keep any sponges etc very clean.