Rust mites causes damage to the peel, however the inside of the fruit is not affected by the mite.  You should be able to rid the mites with a good horticultural oil spray.  Spay early in the morning.

https://news.ucr.edu/articles/2019/03/14/35-million-givaudan-gift-will-protect-citrus-collection

Of the trees that I have, I rate them in order:  Grapefruit, Valentine pummelo, Cara Cara navel, Dekopon,, New Zealand Lemonade, Ponkan all of which are in ground trees.  The rest (lemon varieties, mandarins, kumquats, )  fall into the OK class.

Trees on trifoliate have good to excellent internal fruit quality with all common scions.  Fruit typically have high solids, acids and juice content. I have various citrus cultivars on Flying Dragon, and there fruits are all of normal size.  .

Just an old leaf.  A citrus leaf has a life span of approximately 18 - 20 months. When a leaf is no longer able to carry out all that is demanded by the tree it is quickly discarded.  There is no welfare program for old leaves.  For citrus trees the time of greatest leaf fall is during the tree's blooming period.

In the 2018/19 season, the world's orange production will increase by 4.2 million tons compared to the previous year and reach 51.8 million tons.

One further note:  From the very first sign of flowering, never let the tree's root system go dry.  Doing so will quickly cause the drop of most or even all flowers greatly reducing the crop.

I've attended two best tasting citrus contests, one was at the Alabama Citrus Expo, and the winner of both was Xie Shan satsuma (pronounced She Shan).  It is seedless, easy pealing, early repining satsuma maturing  in October.  I have a Xie Shan satsuma and it is excellent.  Of course Dekopon would be right up there in taste.  Last weekend our local supermarket was selling Dekopon for 3 fruit for 5 dollars.

It is now time for flowering, or very soon  in many areas for citrus trees to begin flowering.  Flowering in citrus trees is the time of greatest leaf fall.  So if you notice more leaves dropping than normal, don't become overly alarmed.

Reading  Greg's link, it says that ground applications moves the insecticide into the nectar.  I removed my post that stated that it did not move into flowers.  I must be more caution   I'll look into my notes, and see what I can find. 

Bicadad, here is what U. Of Florida writes about root stocks for satsumas :

Trifoliate orange (Poncirus trifolata (L.) Raf) is the most commonly used rootstock for satsuma mandarins, especially in cool climates where maximum cold tolerance develops. However, in Florida, where the winters can be relatively short and interrupted by brief periods of warm temperatures, trifoliate orange does not provide consistent protection from cold south of Gainesville.

Trifoliate orange grows well on fertile, clay to loamy type soils. It does not develop a very deep or wide-ranging root system and is poorly adapted to saline or calcareous conditions, but its resistance to foot rot, a soil-borne disease, makes it a good choice for soils with poor drainage. Trifoliate orange is susceptible to exocortis, a virus-like disease; blight, a disease whose causal agent is unknown; and the burrowing nematode, with some selections resistant to the citrus nematode. Many selections of P. trifoliata are available, including a dwarfing rootstock named Flying Dragon.

'Swingle' citrumelo is a cross between P. trifoliata and 'Duncan' grapefruit (Citrus paradisi Macf.). 'Carrizo' citrange is a cross between P. trifoliata and Washington Navel (Citrus sinensis L.). Satsumas are often propagated on 'Carrizo' and especially 'Swingle' rootstocks. This is due to the fact that budding and early tree growth are better for satsumas on 'Swingle' compared to P. trifoliata. The performance of satsuma on 'Swingle' or 'Carizzo' rootstocks compared to P. trifoliata has not been adequately compared, although they are believed to be less cold tolerant than when grafted on P. trifoliata. We have observed 'Navel' on 'Carrizo' and 'Owari', and 'Brown Select' on 'Swingle' to withstand 14°F without appreciable cold injury at the North Florida Research and Education Center in Quincy, FL, when fully cold acclimated.

Chandler is a widely grown pummelo and its flesh is pink.

Nosari7Viper,  if you order the seeds from Japan, would you please return to this post and let us know if they germinate.  Everything depends on how old the seed is and how long it has been removed from the fruit.  Japan is a long way away.  If their seed is fresh than this could help other members of the forum also.