Girls were looking lovely. Now they're not looking lovely?
Could you be more specific? Post a picture or two?
Molasses in hydro? You mean real molasses? IMO not a good idea. If you insist on adding carbs to hydro I'd recommend a supplement. Molasses ferment in hydro, yeast and other critters munch on sugar and use oxygen, create CO2 and in the process raise the PH.
Not to mention the increased possibility of clogging and sliming your system.
I wouldn't say it's too high. As long as the PH fluctuates. 6.5 is considered by many to be the upper limit. But even if you reach 7 and bring it back to 5.5, nothing dramatic will happen.
My PH is always rock steady at 6.5. I have to force it to bring it down and up again in order to have the PH fluctuations. A few times I've upped it up to 7, just to see how the plants will react. Left it like that for several days and nothing happened.
But then, I've never grown plants that need much attention, so the above said may not apply to some of the more sensitive strains.
Being a new hydro grower myself please take all of my advise with a grain of salt.
1st off I tend to be a grower who does not get excited if my plants do not look picture perfect at all times, I tend to be more concerned when I see a problem and it starts to spread. I did a ton of research on hydro before I did my 1st attempt and it is my understanding that the PH range for hydro is 5.5 to 6.5 though the ideal range narrows slightly depending if you are in veg or if you are flowering. I may be mistaken but in veg it is perfectly fine to run on the high end of the range where as in flower it is better to run on the lower end of the range due to what the plant requires for growth during each phase of growth changes. Just like with the different needs with light spectrums are different so are nutrient needs. In veg the blue spectrum is needed more where as in flower the red spectrum is top dawg. Just like light, it is always best to have as full of a spectrum of light even in veg, nutrition of the plant is much the same, when it consumes mostly Nitrogen in veg, it still wants small amounts of other nutrients to balance out its diet.
I would love to have a hydro set up that had no PH swing but in my set up, PH swing is just a fact of life. The bright side of my set up is that it contains 3 gallons of useable liquid and my plant consumes from 2 to 3 gallons per day so the swing is not a big issue for my set up.
In my set up I find that if I keep all the water/nutrients PH'd to around 5.8 I feel I have done fairly well. I just harvested my Huckleberry and while I fell short of what I was hoping to pull off of it, I did manage to pull a little over 12 ounces from 1 plant. I still have to finish my MG plant though I do not expect to pull quiet as much off of her, though I imagine 6 to 8 ounces should be a realistic goal.
During my grow I tried to maintain a PPM within the normal range which is standard amongst hydro growers though I do recall one week when I did have a PPM as high as 2400 which was way more then I would normally feed them but it did not create a major problem though I will say I was sure not to let it happen more then that one time.
Without pictures or knowing more about your grow or what issues you feel you are having, my comments are more to reassure you that even though your ladies may not be 100% it may not be the end of the world. For example, if you were growing under LED lights, your plant will need more cal/mag to prevent leaves from yellowing, I know that this happens because I grow with LEDs yet I do not always put Cal/Mag in with the feeding, one it is expensive when used with every feeding and my plants seem to do fine even though there may be some yellowing in some of the leaves. I try to feed them Cal/Mag at least once a week but that is about it. Would adding cal/mag with every feeding correct the yellowing? Most likely but for me, the cost does not over ride the benefit. My weed that I grow is OK in my opinion and that is good enough for me, some would disagree with my line of thinking, that we should do and spend what ever it takes to get the maximum potency from the plant, but I for one am a smoker who started smoking weed in the early 1970's and pretty much anything I grow today is 100 times better then what was available in the early 70s.
After rereading your original post, it is possible that you were merely saying that you were noticing PH swing in your reservoir and what can you do to correct that issue. If that is the case there are a couple of things you can do to stabilize your PH in your reservoir to keep it from swinging to far up or down. One way is to periodically adjust it either up or down with PH up or down to get it within the range you prefer. Another way is to change your reservoir more often. PH swing is very common amongst hydro grows.