Nah, I do exactly the same thing - except that I drift between 5.6 or 5.7 and 6.1 or even 6.2. This is my first grow with coco, so it's not like I'm an expert, but I think it's a solid strategy. Coco sucks magnesium like a sponge, and in a hydro system (which coco really is) magnesium is best absorbed at PH levels above 6 or 6.1 anyway.
One thing I learned early on is that the less you fuck with your PH, the better off you'll be down the road - especially when you go to flower. One of the reasons for that is that coco is hungrier than hell for magnesium. So, what do you do when you have a mag deficiency? Most people add calmag. So now you have a ton of calcium in your water, you're constantly adding phosphoric acid in the PH Down, plus the extra P in the bloom nutes, and if you're keeping your reservoir temps in the low 60s, the phosphorous and calcium can bind to form calcium phosphate - an insoluble solid that remains suspended in your water, making it look a milky white and depriving your plants of both vital nutrients because they are no longer in a form that can be taken up by the roots.
So, yeah; each rez change I start out on the low side, and deliberately let it drift over the next several days if that's what it wants to do. I'm finding that the coco does a pretty good job of buffering the PH itself, if you've got a healthy root zone and a sensible blend of nutes and additives, it doesn't fluctuate very much. If you start to see sudden changes in the PH, that's a sign you may have a problem. Normally, it tends to drift upward at a fairly slow and steady rate. I still check the PH at every feeding, but it almost feels like a formality sometimes. I like to play a game where I guess what the PH will be based on the last reading and how many days since the last reservoir change, and I'm usually very close.
