About a month ago I purchaced a Moro orange and a Fukushu kumquat from a local store, both of which were originally from Duarte Nursery. I'm wondering if I should repot them, I can see roots if I look into the drain holes of the Moro and the Fukushu has actually put some roots out into the drip tray. I'm also not too sure about the potting mix that the nursery used, as far as I can tell it's just sphagnum moss and perilite.

Since the local envroment is probably very different then what their use to, I'm wondering if I should let the citrus get used to local conditions for a while. I'm also a bit leary about re-poting, the last commercially bought citrus I repotted (a centennial varagated kumquat) nearly died due to my poor choice of potting medium (ordinary potting mix with about 1/2 a part bark chips).

Oh, And I should mention what I'm going to use to repot them in, I've started using 3 parts fine pine bark, 1 part sphagnum moss and 1 part perlite. So far all the citrus I've repotted into it seem to have done well, however I've only been using it for a few months so I'm not sure how it'll hold up.

A picture of the two citrus, Fukushu on the left, Moro on the right.
http://imgur.com/KMEKc.jpg

I believe you are always supposed to re-pot if roots are coming out the bottom.

And it would only take a glance to figure it out if you can slip the tree out of the current pot. If you have had the trees for a month then it seems enough time for them to adjust to their new home.

I agree if you can see roots coming out the bottom its time to repot=
water the tree first and come back in 30 mins,squeeze around the container providing its plastic...tip on it side and gently remove...have your soil mix prepared(i use a 20 litre bucket)....If you see a dense root ball....tease out the outer roots with your fingers and place in the new container.....Make sure the new pot is no bigger than 4 inches around the rootball...ie 2 inches either side and below...That should be fine for one years growth.
There is no need to use a bigger pot...Its a false economy and your better to pot up in stages.....less chance of root rot....when your tree develops a big rootball,you could pot up a bit bigger pot as the tree has a more dense root system.Water well and dont feed for at least 2 weeks to allow the roots to settle in...dont leave in saucers full of water...keep on pot feet for aeration.Dont leave in direct sun while settling in either....when you see new growth,then add some slow release fert or your favorite soluble feed at half strength...take it easy on young trees...Good luck!
p.s your mix sounds fine...you need a compromise between water holding capacity and air...I find my mix compresses about half to 1 inch over the first month...its compaction you need to slow,so the roots can move in and take the air spaces...I would even go a bit more perlite...i use coarse grade pummice in Nz as it holds air spaces inside itself.Volcanic rock i believe.Perlite is extremely good at avoiding compaction plus pests dont like it! I saw a shopping Mall in Israel that grew citrus in big pots with only fine and coarse grades of perlite and the containers were see through.Amazing! couldnt find your pics from above.

laidbackdood , I learn something for myself , thank you

here is the picture

I've found soaking doesn't do much to get the old potting soil removed from the rootbound - roots. I find it best to get your fingers in there to massage the old soil away - that and rinsing a lot helps get down to the roots.

I agree with much of what Laidback writes above. I only differ with watering the container before transplanting. I find that if you let the medium dry out a bit before transplanting , it holds together much better when the tree is removed from the container.

Many growers prefer to purchase bare root trees in the beginning, such as trees sold be Four Winds Growers. With a bare rooted tree, one can start out from the very beginning growing in a CHC or bark medium. It is difficult to purchase a container grown tree and bear root it, without causing some damage. As has been mentioned before, most nurseries use 3 part bark, 1 part peat moss and 1 part sand as their container medium. This is a good medium to use, but it has a one big draw back. The problem is that the medium has a usable life span of approximately 1 year. Therefor, if the tree is not purchased soon after the nursery has potted it up, the medium becomes compressed and difficult to remove. As Sludge writes, when transplanting into a larger container, it certainly is not wise to fill the empty spaces with a fast draining medium like CHC, when the tree's root ball is in a tight root filled ball. The water will naturally take the path of least resistance, and just run down the sides, leaving the root ball very difficult to water. Further roots tend to resist growing from one type of medium into another type of medium . - Millet (534-)

I tried a fair few times with chc and my trees died...did the cation exchange thing....I washed away all the old soil very gently too but i just had no joy...I figured the trees looked pretty healthy in the pots they came in....so i re focused my attention on growing in a similar medium but with improved drainage and aeration plus the ability of terracotta to breathe.
Millet...You were right about my transplant....it has continued growing as if nothing had happened....I have come to the conclusion that growth stopped on the previous occassions due to transplant shock.....Now i just disturb the outer roots and add fresh mix and try not to mess with the rootball too much..True what you said about the watering...the other day when i transplanted i didnt water before removing from the pot and it does hold together better(just realized now!) Its all good fun.
with ref to your new mix and the old mix...I had a strange theory but it could be garbage LOl....disturb some of the old medium and mix it in with your new medium to help the two to blend(different bacteria)...I felt the complete change of environments from mix to chc shocked the hell out of my past attempts...now i go more for a balanced mix of in organic and organic components to reduce compaction....Perlite is awesome for that(although i am not using that now)and it improves drainage if that is a problem...water clings to it too....its like the mix has suspension Good luck
p.s those trees look healthy at the moment.