This link might help everything you wanted to know about growing citrus trees. Since you are in S. Africa you would have reverse seasons so you may have to change the months that you feed your plants.
I have trees in pots and 5 in the ground. I have to fertilize the ones in the pots more often than the ones in the ground obviously. I use citrus fertilizer on everything because 1) its acidic and good for the alkaline plots 2) it contains micros 3) I'd rather have fewer bags of fertilizer around and this one is pretty good and I can use it on just about everything.
After flowering and right before the new leaves come out that is when I give my trees the first feeding that will be higher in nitrogen. the second feeding is just about when I expect to see flowering, I will use a lower N higher K (my soil is already high P so I try to stay low on that), again after the fruit starts forming (I will also up the watering at this time a little more) As the fruit starts to ripen back off on the water so as not to dilute the flavor. I only fertilize twice a year for the trees in the ground.
For the potted tress, I use the osmocote as a slow release and I will give a tablespoon of citrus food for every inch of tree trunk when the tree is in active growth. Some of my citrus trees like the Bears lime will only fruit once a year, but the calamondin will fruit up to three times so I need to feed the calamondin more frequently.
I pot my citrus in cinders that does not retain any fertilizer so I need to fertilize more than you might need to if you are using a different media. I prefer cinders because I have trees in pots long term. Peat based mixes have to be repotted more often. I have citrus in 20 inch pots of cinder that have not been repotted and have been in the same pot for 16 years. Cinders do not break down well, they remain well drained and the roots remain well aerated. The pots are difficult to move and the oldest tree is 5 ft tall (potting keeps them dwarfed), so they pretty much only need to be weeded and tipped once in a while to make sure they have not gone to ground.
I also keep sulfate of ammonia, dolomite lime (I rarely need it) for pH adjustment, I can use compost, vermicast, or manure to accomplish the same thing and it is better for the plants in the ground, osmocote/nutricote (slow release fertilizer), and water soluble fertilizer. (I can skip the specialty fertilizers unless they are on sale, I prefer low or no phos. fertilizers since the soil in all of my plots are adequate or very high. I keep nitrogen, because it is best to give that in divided doses, and I find that urea is hard for me to apply unless I mix it in with the compost or potting media. 46% N is easy to burn plants or cause issues with germination).
Happy gardening in Hawaii. Gardens are where people grow.