carbon filtration can change ur ph drastically or it can make it perfect (6-7), it depends on so much- what kind of filters ur using, how many in the sequence, wats in ur tap before u OM it in the filters, wat ph ur tap is before filtration of course, how its stored, water pressure, things like that.
for the most part tho, reverse osmosis or carbon filtration will not make a huge difference in ph, but just know that it can. and u will need to test ur water definetely b4 using it.
and preferably have an access port Aka, bypass valves, before and after each filter the water runs thru- that way if the ph is getting jacked up, u can test the water after each filter so u know which filter is throwing it off so much.
if ur only using one filter u would prolly wanna boil ur wa wa first for best results and so u dont burn out ur filter too fast.
idk boiut ph lock, but if ur manually filling ur buckets, once your ladies get to flower and they are takin up a gallon or so a day u wont need to adjust ur ph before u fill it(given ur water is the corrent ph in the first place) and given u are replacing that gallon daily.
once mine get big i hardly ever adjust ph, cuz they drink it up before it matters lol, i hardly ever adjust ph anymore at all actually
Cheers!