Great, you're using Foliage Pro. I'd go with a heavier dose, once or twice a week. With my Meyer Lemon, I comfortably fertilize with 1.5 teaspoons per gallon of water, once a week. I wouldn't want to re-pot so soon....and I hate to say it. Perhaps others will comment on the containers. I'm looking at the plants and anticipating more growth this season. There is an interesting debate regarding terracotta. I see that you're located in a zone 6, which means cold Winters. Many folks in the northeast, for example, are finding that black plastic containers help keep the roots warm and the plants more vital during the colder months, including the Spring transition out of doors. I hope some other growers will chime in. As for the Neem treatment....yes, treat all of your Citrus. I like to do lighter Neem treatments, repeated three times, three days apart. That said, the stippling on the leaves could be *old* damage, and there might not be any mites currently. But Neem won't hurt, so you might as well be pro-active. Josh

Some of that looks very similar to aphid stress I had least year shortly after planting out. But it's hard to tell with the color shift. If you only did one treatment, it's likely that you didn't get everything, the Neem especially needs to be done on a recurring basis. I tend to alternate with the soap and then Neem 2 days later, repeating the cycle for a couple of weeks for my indoor houseplants when I see a buildup of aphids or mites. Don't know about the power of those grow lights but one of the things the Neem bottle says to look out for in outside use is burning the plants by spraying them in the high sun. Could that be a factor here? Or maybe could your treatment have been too concentrated? The soap especially needs to be pretty diluted. Can't help you with the nutrient side except to say to peppers don't need or like all that much nitrogen, and that aphids can be attracted to higher N levels. But seeing as hydroponic is a whole different thing when it comes to nutrient balance, that may or may not apply.

Jue Shei: for the 1st picture, you are right that the whole plant is not pale, but only the upper leaves. I look at your 1st pic. three times, and it looks like iron deficiency (dark veins on pale leaves). See below excerpt: "Iron Deficiency: Caused by High soil pH and salinity. - High Phosphorus, Manganese, Calcium, Molybdenum or Zinc levels. - Soil low in organic matter & Insufficient drainage. Leaves become yellow or near white between their veins. Stunted growth." From Straw: For your 1st pic., it looks like high soil pH (wood ash has pH of 13), plus salinity or high salt (wood ash is very high salt). If you did NOT put wood ash in the pot, it can also be poor drainage. My rose in soaking wet clay has that problem during heavy rain. If water cannot drain fast from a pot, upper leaves can have iron deficiency (pale background with darker veins). If it's a high pH problem from topping with wood ash, then scrape off the topsoil When the soil inside the pot IS NOT changed every 2 years, then the soil becomes compact and water can't drain fast, roses will turn pale. My most dark-green roses are with NEW potting soii which is fluffy and has air for root growth. If your soil is more than 2-year-old in the pot, then change to NEW SOIL will help. Old soil in the pot for more than 2 years accumulate too much salt, then become compact so roots have zero air, so leaves turn pale. From the web: "An ideal soil contains 25 percent air, 25 percent water, 45 percent minerals and 5 percent organic matter."

Others on this forum have had good success with neem oil, although I've never used it personally. I have been battling a spider mite outbreak on my indoor citrus. Two products that I find work well are: Safer's insecticidal soap and Monterey horticultural oil. Any oil or soap must directly contact the mites (and their eggs) to be effective, so excellent coverage on the top and bottom of the leaves is required. https://www.amazon.com/Monteray-6290-MONTEREY-HORTICULTURAL-CONCENTRATE/dp/B001RPVUCY/ref=sr_1_2?ie=UTF8&qid=1495043455&sr=8-2&keywords=horticultural+oil https://www.amazon.com/Safer-Brand-5118-Insect-Killing/dp/B00192AO90/ref=sr_1_2?s=lawn-garden&ie=UTF8&qid=1495043593&sr=1-2&keywords=insecticidal+soap