fertilizer need and leaf drop

[35ppt]

   I have two kumquats. Both are in promix, amended with perlite. When I removed the nursery soil and repotted in promix+perlite, I did NOT add any CRF.
   Summer fertilizing was a bit erratic, because if they got rainwater, then I didn’t fertigate. Now that they are indoors for winter (since about November), I have been fertigating with DynaGro FP at the ¼ tsp/gallon rate. So, every watering, they get fertilizer.
   I also have a limequat that is in whatever the nursery mix is, including CRF. Also been fertigating this since moving indoors .
   My nordman nagami kumquat looks good, although the petioles are a lighter green than the leaf. Maybe that's normal?
   My meiwa kumquat has small yellow spots on the leaves, and has dropped a few since coming indoors.
   My limequat looks the worst, with yellowing from the base of the leaf, down the center. It dropped some leaves shortly after moving inside, then mostly stopped. But it is starting to drop again.
meiwa:

limequat




I know about spider mites; I am now seeing them on my naners, but not on the quats (yet).
The yellow spots on the meiwa are larger than what you usually see with mites, though.

So my questions are:
Should I fertilize at all over winter?
Are you supposed to use CRF and the diluted FP?    
Do these particular yellowing patterns tell me I have a specific nutrient deficiency? I’ve looked at a bunch of online resources and am not seeing these particular yellowing patterns associated with nutrients.
I've just learned a bit about pH, so in the past few months I have switched from my tap water pH 7.6 to rain or RO water at pH 6.0.

[Millet]

Does CRF stand for controlled release fertilizer?

I would add, that citrus are heavy feeders, requiring more nutrition than most plants.  1/4-tsp per gallon of a 9-3-6 fertilizer does not seem enough for citrus. To answer your concern about the yellowing of the limequat leaves as shown in the picture, first let me ask how old is this tree?   

[35ppt]

yes, CRF = controled release fertilizer.
From my reading thru forums it appeared that people are using FP and CRF?? If so, I should probably add some to my pots without it, unless winter is a bad time for that. These are growing in my house.

I got the limequat last summer as a 1 gallon and it is currently about 12" tall. It has flowered a few times but not set fruit. Since it has just finished flowering I am once again thinking of repotting it to replace the grower mix with mine. I will probably use ProMix since I haven't figured out how to use 5-1-1mix yet. But again, should I do this in winter?

[luak]

Make sure you do not overwater and make sure your ph water is around 6-6.5. I use small ph paper strips you can buy. I think they are 100 for about 10 dollars

[Millet]

People on various forms say repotting should only be done in the spring.  Personally I have repotted in just about every months of the year with no problems at all, you can do as you feel best for your tree. The 5-1-1 mix is pretty straight forward. It is a blend of 5  parts small sized bark, 1 part peat and 1 part perlite. I don't use it, but it seems to be a good enough mix, especially for smaller sized trees.  For large trees in bigger containers, I don't know if it could give the tree enough anchorage to hold up a tree in fruit.  Looking at the limequat's leaves I would say it could possibly be from under fertilizing, or it is possible that they are just getting to be old leaves ready to be discarded.  A citrus tree does not waste anything.  When a leaf becomes to old to perform it duties, the tree removes the nitrogen from the leaf for use elsewhere in the tree, then discards it.   That's why old leaves begin to turn yellow before it is discarded.  Citrus leaves have a life span of just a little under 2 years (about 22 months). I can't say for sure as I have never used Foliage Pro, but 1/4 tsp/gallon does not seem to be enough nutrition for citrus variety.