Zeririerkal, did you follow container directions when you fed the plant? What I'm asking is, is it possible you overfed?
Does the pot have drainage?
Feeding every 2-3 weeks, (unless you divide the recommended dossage,) is a lot of food. What type of fertilizer did you use?
Since you noticed the leaf curl the night after you fed, I'd say you're over-feeding.
Overwatering symptoms are yellowing leaves. Yellowing and then drop.
Make sure you're using a pot w/drainage holes..You may need to flush the soil, which means, running water over soil to flood out salt build up.

The only other time I've seen leaves drop like you're plant is doing is when THE plant was in direct sun in a very hot room..(this will happen if it's recently been moved to a location like I've described) Good luck, Toni

Curling down leave is not one of the various symptoms of over feeding. The leaf curl could possibly just be from the cloudy, dull weather. However, my guess is there is nothing wrong with your tree. One word of caution...A citrus seedling at the age your tree is, is VERY prone to root diseases and stem rots. Be VERY CAUTIOUS about over watering your little tree. - Millet

I had a friend who grew a certain, unmentionable plant...He assumed adding a tripple dose of plant food would hasten its growth..The next day, leaves were all curled, lol, only they never uncurled..that was the end of his plant, too..Toni

I'm using miracle grow all purpose plant food 24-8-16. The directions on the box say feed evey two weeks. I do have holes on bottom of the pot and i'm using rain water to water the plant. Also few weeks ago the soil in the pot has began turning little bit greenish color on the surface.

Zerirerkal, sounds like algae..This has nothing to do w/feeding, but wet soil and sun. It's too bad fish (algea eaters) couldn't live atop soil..LOL..J/K..
It could be your soil is too heavy..are you using a rich, black soil without other mediums like Perlite and/or sand? If a soil is too heavy, it'll take longer to dry..
Because ferns require a good amount of water in summer, I keep the soil wet, and have had see algae on my soil too..It won't harm your citrus though..but constant wet soil will.
I wouldn't unpot right now, (if leaves are still curled) but as soon as plant resumes health, and if you're soil is too heavy, then I'd think of adding other mediums..
How are the leaves doing? Are they still curling?
One other thing..On the Miracle Gro box, there's two feeding dossages..One is for feeding monthly, the other is for feeding every two wks..If you feed every 2 wks instead of once a month, then they advise dividing dossage in half..Actually, when I feel plants, I use even less than they recommend. Remember, they want to sell fertilizer. This advice is also written in a good number of plant books..Good luck, Toni

The fertilizer you are using is really not all that far off, (if it is an ACID TYPE FERTILIZER). I have seen much worse. Your fertilizer (24-8-16) is a 3-1-2 ratio, and the ideal ratio for citrus is a 5-1-3 ratio. 5-1-3 is the ratio that citrus roots absorb nutrients from the growing medium. Also you need to look at the label on the fertilizer bottle and see what the acid reaction (pounds of acidity) is for your fertilizer. I do not know if 24-8-16 is an acid type or a basic type fertilizer, and you need to find out. Lastly when you see green moss or green algae growing on the surface of the medium it is a SURE sign that you are keeping the soil to wet. So either your watering to much, or your "soil" is holding an excess of moisture for to long of a period. You might look through this forum for information on CHC (Coconut Husk Chips). They are a popular growing medium that gives EXCELLENT results for citrus culture. You will find hundreads of threads on this product. It will be well worth your time to do so. Use the search box in this forum. Happy to see you posting on the citrus forum, good luck to you and your tree. If any of us can be of any further assistance to you please ask. Take care.- Millet

I can't offer a reason.. but I had similar thing happen to me yesterday. I was flushing 4 month old seedlings as a few plants looked like they might be suffering salt buildup. I flushed them several times. I noticed 3 of my plants do this. the top young leaves curled under very tightly. and by this morning they have uncurled.. the ones that curled were kumquat and clementines. none of the others had this same reaction but they all received the same water. the ones that curled were not the 2 plants that look like they are suffering salt buildup. they all look healthy today.. save the bit of yellow on the couple with salt buildup. I'm gonna start a new post about them..

I offer a "theory".. After much consideration on this.. I have developed a theory..
Where is your tree located? I have mine in a full sun in a window. I wonder.. if drastic temperature change could affect a young inside tree like this? as soon as the sun goes off my trees they are exposed to AC house temperatures (not so much right now as window AC is having trouble cooling off 115* outside temps and even night temps in this full sun room are at 80+*F).. and after watering the soil temperature is even more susceptible. I have been watching my soil temps again. checking several times through out the day, day after day noting how long since I watered.. In the window during the day the soil temp can reach as much as 100* and drop to 70* at night maybe even less.. the variation lessens the further away from watering I get.. the soil holds the day temp longer when it is dryer. and it takes longer for it to heat up.. water acting as a conductor of the heat/cool. and being they are younger plants they are even more susceptible to this temperature change.. When this happened to me it was even more dramatic as the further away I got from the window the cooler it got and it was nice an cool over at the sink I used to flush the trees.. and I used nice cool water to flush them unlike the normal water that has sat and reached room temperature and then some since the jugs are real close to the window.
How does that sound to the PPL in the know in here??? For me it is JUST a theory as I have a minute amount of knowledge about citrus and their habits and needs..
Any other input to this theory is welcome!!
Gina *BabyBlue*

I have a young tangarine tree newly planted. It has grown some and has new lite green leaves. My concern is, the leaves are slightly curling. Not down as others spoke of, but up. Otherwise looks healthy. Should I be concerned? I have watered every third day, as the temperature has been extreme. ninty plus degrees. Mary O.