Help ph probe calibration

[wil0311]

I just bought a calcium reactor. I have packets of ph calibration solution of 7 and 10. Now I want to run the reactor at around 6.6 ph. So my question is can I calibrate my probe with 7 and 10, or do I need the 4 and 7 solutions? I would like to know if the probe is accurate when lower than 7 ph because I already calibrated it with the 7 and 10 solutions.

Thanks for your help.