If you have recently repotted, giving it fertilizer was a mistake. You need to leave it around a month before using fertilizer. Sounds like the roots may have been burned. Flush the pot - water it with watering can after watering can of water, about a half dozen times, to get all of the fertilizer out of the soil. Position the plant back in the south facing window or use the grow light, then put it on a gravel tray. Mist daily. Check for bugs and buy a small humidifier if you can. Do not feed it with fertilizer until it is showing good signs of new growth.

Flush the pot, position in good light, make sure the root temp doesn't fall below 65F (very very important if positioned in bright light) keep th air humid and check regularly for bug infestations.

Keep us posted on your tree. Always nice to hear from people with trees that got better rather than just trees that need help :)

I would check again for spidermites, they always come back!

If when you first got it it was very dry, it is unlikely to make it loose its leaves quickly,most times you can dry them out to dust for a week or so and they still keep all there leaves, If now you have been keeping it damp that is more likely to cause leaf loss than being dry

Dropping of leaves is normaly due to the compost being too cold, or root damage / incorrect air temperature / too low humidity / lack of air due to wet compost or to an insect on the leaves . When the compost is too dry the leaves normaly fold or curl slightly more than fall off

if you had spider mites they were probably why the leaves dropped, even though you couldnt see them as there were not enough to see, they probably were still there

After repotting as aesir32 says, your not supposed to fertilise them for a short time, but i do and have had no problems, with the fertiliser you are best getting a citrus fertiliser as unlike a lot of plants they realy like the correct levels, especialy of micronutrients such as copper,boron,zinc and mgnesium etc.

If you are using a growlight, you need to make sure the roots are warm enough or the leaves will fall off as they cant get rid of the heat as the roots are not active enough, you need the roots over 65F better over 70F for normal levels of light , if the lamp is bright/powerfull/close to the leaves you would be better with closer to 85F root temperature.

Starloc,
When you are saying that root temps need to be above 65, are you talking for daytime highs while lights are one.
It is ok for temps to lower in evening right?
thanks

If temps are lower in the evening its Ok, unless the plant is under artificial lighting. If the roots are too cool when there is bright light on them, leaves drop. If its pitch black night and the root temp is only 55F don't worry so much...but make sure they are warm enough for when the sun comes up and hits the leaves. Remember, soil takes longer to warm up than air!

Its best to keep the roots warm though to stop the plant trying to go dormant, in the morning you need to warm it up before the light gets on it so easier to keep it warm, if you use the lights its best to heat the pot a bit first, if you have no heater mat, put it on something like a radiator for 10 min or so first

You want it over 65, preferably 70F or more before the lights are on it, if its 50-60F it is too cold to use growlights, depending on the plant, with a meyer lemon or any of the lime trees or kumquats, they like to be warm, very warm root temperature, they dont care about room tempertaure unless it is actualy frosty but root temperature they like close to 90F to prevent leaf loss.

Starloc,
Are you talking about keeping the temps at this degrees day and night, or are we suppose to allow for a cooling period at night?
When my lights go off at 700pm, the room cools to about 60 degrees by the am, then warms again to about 75 degrees.
Thanks alot

The roots do not need a cooling period, they can be warm all the time, they dont need to be so warm in the dark, but they will be cool before the light heats them that can cause problems. constantly warm roots seem to reduce winter leaf drop to no leaf drop.

The cooling period `chill hours` to make it flower next year is only related to the leaves/air temperature, the roots can stay warm, if the roots are warm then there will be no loss of leaves as long as it gets light during the day.

I used to turn soil and air heaters off at night, so they cooled a bit to rest the plants, but there is no need so i dont do it now, just use a thermostat for the soil, and turn the air heater off to let the room drop right down to get chill hours

Starloc,
The reason why I ask is because the local greenhouse worker said that all plants need to cool off at night in order for them to utilize the sugars they produce correctly. He even said that if I keep the roots warm all the time that I am inhibiting nutrution uptake and could stunt growth. He gave me the example of hot summer evenings when the soil does not cool off at night and then in effect, grass stops growing until cool nights return again.
What do you think? Thanks alot

Starloc,
Oh ya. Come to think of it, I think tropicals such as citrus require warmer temps than local vegatation up here in the north.
For instance, I was loosing the leaves and even branches on my "Duke Jasmine",, one I keep in full sun on a window sill. I thought it was going to die, until, that is I used a heat matt to warm the soil and keep the roots warm by night also. Now it is producing flowers and in a growth state. I never had sucess with this type of plant until I warmed the pot by night...HUM....Interesting!
Maybe, for alot of us who are keeping our plants in south facing windows to get as much sun as possible, we are , or at least I am forgetting that by night, the closer our plants are to a window up here in the wintery north, the better chance the pots they are in, cool off much more than one may think or want, and especially if they are on a window sill, even though the room temp away from windows can be quite warm..Hum.....I just had a apifany.:-)
It can get mighty cold near a window this time of year, even a couple of feet away from it.

Eureka! Success! My lemon tree has not only stopped dropping leaves, it is producing new leaves!!! The spidermites have not come back. My growlight is positioned 18-24 inches away from and lightly above my tree, and stays on from 10AM to 4PM. I have continued to use the Espoma fertilizers. Hooray!