Yes, that is an acceptable range, but nothing is written in stone. In a low nutrient tank the Alk levels recomend are around 7 or 7-8 dkh.
The OP do not have a LNT , the phosphates levels are high. Need to be around 0.04 ppm.
Beside that, as Dong mentioned, Red Planet Acro grows a big encrusting section from which branches start to growth. I know that by fact because I have 2 Red Planets at my tank. One came from Dong colony almost 2 years,ago. And it took a while until it started to really growth.
Bottom line, the range 8-10 dkh as comente is not bad, but neither is the best. Of you really plan to keep many acros I will suggest to move to ocean levels parameters with Phosp around 0.04 ppm and Nitrates 0 or a little higher. Many fish and a strong feeding to keep your Acros with food and colored. The LNT can have a negative effect if you just keep it like that (color fading, for example).
The most important thing is that : " if your Red Planet is growing in your conditions or any other is growing with your tank parameters DO NOT CHANGE THEM, STABILITY in the long term is what will make your SPS happy, mainly Acros ".
Best !!