Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
2-3 degrees of each is just fine for most plants.
Monitor the GH through the week. If a hobby test cannot tell the loss, then it is insignificant. If the plants are growing so well they are removing significant amounts of Ca and Mg, then I would just dose GH once, mid week.
Allow the tank to run with just the KH you have and see if the pH stays, not the same, but follows a cycle through the day with the high and low being about 1 unit of pH. For example, from a low of 6.5 to a high of 7.5.