I saw other postings mentioning spider mites but I just don't see them. Thanks, I will move it outside and followup with neem/HO spray and report back.

It is definitely spider mites; you can't see them without a 10X loupe. Spider mites like dry and dirty (dusty) conditions. A wash with a hose or in the shower once a week goes a long way to controlling them. Outside is easier to control because it is not so dry; and is easy to wash with a hose, when you are watering.

I just dealt with them on my citrus. The first sign I got with them was twisted leaves and loss of the lush dark green color on the leaves. They made all my citrus trees look like crap and set them back months in terms of growth.

As a result I'll be treating my trees with a very mild insecticide/miticide every month when indoors for the winter as well as upping humidity

Agree with johnmerr, definitely spider mites as the leaves look just like my calamondin's when it got infested this past winter. The mites and webs were visible and about half of the leaves lost most of their green color. From a distance the tree looked silvery. I basically tossed it out into the cold and rain and amazingly it's recovered. Most information say the leaves will turn brown and fall off but I think the chlorophyll is coming back as there are spots of green on the leaves and the tree looks less silver.

The leaves don't recover, at least in my experience. They eventually drop. The way the light hits them sometimes makes it look like color has returned but it's not so.

As soon as my tree put on new growth I removed a good portion of the damaged leaves so new growth can replace it

Spider mites are very difficult to see and may not be noticed until leaf damage and webs appear.

The leaves do not recover but drop as a result of old age. I would not remove leaves because they are still good, functioning leaves and the tree "knows" when to drop them.

Everything I've read says that damaged leaves will not improve so maybe it's just wishful thinking that's got me seeing the green bits on the bleached out leaves slowly expanding ;-) .

It dropped a lot of leaves but there's new growth with flowers and fruit developing so it's definitely recovered from the spider mites. Maybe a few weeks behind in growth but could also be due to the lousy spring weather we had.

JOhn ng, take your kumquat outside and give it a good spray with water. If you can leave it outside for the summer, it'll do wonders ;-)

Yes, the sun and fresh air should help. You may need more light to get more leaves, although my kumquat is in full sun and not doing a lot of leaf growth.

Remember to acclimate gradually, though. Then in the winter, mist with water and use a fan to circulate air, especially towards the leaf undersides.

I moved it outside. Any tips on when it is time to move it back indoor? Is there any way to prevent spider mites before moving it back indoor?

thanks everyone.

Some people say move them indoors when night temperatures go down to about 40 F, others say move them in while it is still warm, like night temps in the 50's so that the trees do not have as great a temperature shock going indoors. I do the former.

To make sure there are no insects on my trees, I spray my them a month before bringing them in with neem oil, again two weeks later and a final spraying just before bringing them in.

Looking better already! New leaves are looking healthy.