This looks like a nutrient imbalance/pH/water issue to me. The difficulty in this is that the soil pH, fertilizer and fertilizer schedule, as well as water all interact to create potential deficiencies or excesses of certain nutrients, which can lead to pale leaves, dark edges, and tip burn. Without specialized testing there's no way to know right off what needs to be done. All you can do is experiment and hope for the best.

The fertilizer i am using is Dyna-Gro Foliage Pro 9-3-6. Do you think this could be part of the problem?? I live in oregon which generally has very good water quality so not sure if it is the water.

Terrilou: The last plant is Mac's Scorching Sun :-)

I have no answer for you but I just wanted to wish you good luck in getting your plants back in good health. I use dyna-gro Grow which is a more balanced fertilizer.

Are you feeding by misting your plants.? I'm wondering if you have mildew on your leaves. I've never seen leaves that went white like that. African violets are understory plants and prefer bright indirect light, meaning they may be getting too much light. Check the undersides of the leaves for possible spider mites.

Are any of your non variegated varieties showing the black? It may have something to do with the genetics of variegated varieties. I also use Dyna-Gro Pro 9-3-6. I have only one T8 fixture & when installed, I checked the light output with a meter. . . it was really bright, in fact too bright for violets, so I placed other light loving gesneriads on that shelf. After a couple of months, the intensity had dropped & I could grow violets there.

I agree with seamommy - on the one plant it looks rather like mildew. Too much light which results in too much humidity as it appears you water your plants using wicks and this would mean there's a lot of water available to turn into humidity. perhaps this is the cause? Just a guess. But it also looks like the center leaves are fine. Maybe its just old leaves that need to be removed.

hmmm.... more questions :-) It seems to mostly happen on the variegated varieties. Only one or two of the non-variegated ones have black tips. It also happens to the older leaves the majority of the time but not always. I'm seriously considering going to manual watering as I have one that is not wicked and it is doing the best by far. The wicks seem to either suck up a LOT of water or not work at all. I can't seem to get them right.

I only feed through the water in the reservoir. no misting. i even stopped fertilizing for a few months to see if it was too much fertilizer causing the issue.

I see a lot of algae in your reservoirs. Could that be causing problems?

Not likely, Melody Rose; algae in the reservoirs may be unsightly to some, but the violets won't care.
Kaity: Have you tried moving all the variegated plants to the ends of the shelves where the light is just a bit less intense? As to fertilizer, I had some issues over a year ago while using Dyna-Gro Pro, but the problems were not like yours - no blackened leaf tips as your photos show. Do you have a local cooperative extension office where you might take one of your plants for evaluation?
I surely hope you can find the answer - Good luck!

Thank you guys. I figured it wouldn't hurt anything to take care of the algae so got some Physan 20 and cleaned everything else. worst case scenario the plant rack looks nicer.... I moved the light further away from the plants about a month or two ago to see if too much light was the culprit. I will try moving the variegated varieties to the outside now too. I went through them all and it is only the variegated ones that are having issues with brown spots on the edges of the leaves.