Here is a pic of the leaves cupping.

Yellowing of leaves and cupping both point to overwatering. The root tips start to rot and cannot take up nutrients. I would pull the tree out of the pot, brush/rinse off the soil and inspect the roots well for any mushy tips. Prune those off and repot, watering only when the soil several inches down is dry. I'm not sure where you are but here in Southern California, I haven't watered in several weeks, the soil in my containers being plenty moist.

Under watering will show by the leaves being shriveled, and the leaves will return to normal several hours after good soaking.

Your soil seems to be very dense which is terrible for potted citrus. the mix is holding to much water and is causing the roots of the plant to rot and die. I suggest doing what "Fireballsocal" said but use a mix with better drainage. The 1:1:1 and 5:1:1 gritty mixes which you can read about on this forum are perfect for potted citrus.

I have repotted my lemon and Mandarin into gritty mix, but was going to leave the lime until the end of summer, as it was doing so well.

It has been dry here (no rain in the last 20 days and full sun) and i have been paranoid about over watering, so had hardly watered it in that time. That is until this week where I have done a deep watering twice. The soil had been dry, as I tested the soil with my finger.

Are you sure it is over watering/moisture? If 100% I can transfer to gritty mix, just want to make sure it is that.

Cheers,

Ben

Without pulling the tree out of the container and visually checking the roots, I couldn't say for sure it's overwatering. Yellowing leaves could also be a sign of a lack of nutrients so fertilizer would fix that. To my limited knowledge though, cupping leaves signal overwatering.

When is the best time to repot?

It has just gone through a big growth faze, so is it best to wait until Autumn? or should I just go for it now?

I am in New Zealand, so our seasons our upside down.

Cheers,

Ben

Cupping is usually a sign of not enough water, not too much. Commercial orchardists actually use this feature to know when to increase water, here. The dropped leaves just look like normal aging of older, lower leaves. I wouldn't worry. If you're concerned about your potting medium being too heavy and retaining too much water at the bottom of the pot, find out. Push a stick all the way down to the bottom of the pot and pull it out. See how wet the end of the stick is. If it is really wet, you may have to re-pot now, so you don't end up with root rot.

Patty S.

Thanks Patty for putty my mind at ease.

I will definitely re-pot before the winter, as it is crazily wet here in winter and it has caused issues with my other two citrus.

Cheers,

Ben