I'm running some autos as well. A dozen outside in the ground and 3 small ones indoors to breed with. Spraying one with STS to force fem pollen and starting to see 'nanners emerging.
pH pens don't seem to read these nutes properly so you shouldn't be adjusting it. The pH will find it's right spot once in the pot and as they are hydro nutes pH 5.5 is what I aimed at in DWC before pH Perfect came along. Your water sounds fine so trust the technology and just mix then feed.
Autos continue to grow as they flower so at this stage they will still want ample N so I'd stick with a 1-1-1 ratio for feeding then the P and K are helping with the budding end of things. I'm still working out the best way to feed autos myself while getting heavily into more organic growing using ProMix HP as my base.
I barely use any CalMag with RO water that's about 3ppm but do add some Epsom Salts now and then. In flowering the plants like extra Mg and the S in it is the 'secret ingredient' in many bud boosters. I love Big Bud myself but only use about half they say to use. Just read a paper today that supports the idea that we use way too much P and K for optimal growth and actually reduce resin yields.
You say you use BioBiz CalMag. Do you also use their soil? As ProMix has zero nutes it has to have nutes right away but with real soil that has lots of nutes you need to feed hydro nutes at lower rates.
Like I said I'd wash a little water thru it. Maybe half the volume of the pot for runoff and skip a feed. Then do a 2ml/L of each with a tsp/4L of epsom.
How much does that water cost you? I'm paying $3.49Can for a 20L jug and we use it for drinking water as our tap water comes out of a dugout on our property and is unfit for human, or plant, consumption except outside in the garden. I bought all the stuff to build my own custom RO unit but haven't got around to installing it yet. Soon tho I hope.
Big thunderstorm tonight that broke 4 branches off my 5 outdoor auto plants. A good 3 or 4 oz of yield lost there dammit! Wife says I told you so. Should have made that windbreak. Hate when she's right.
Need to set up a cover as well. Can get nasty hailstorms this time of year. Just another month to go. Same strain as last year and started at the same time and they were chopped Sept. 11. 6oz each.
I took all the fans off before taking this pic last fall. Chopped the next day. The middle one is an unrelated CBD auto.
Poor girls all beat up.
3:30 so off to bed for this old fart.