The Tropical Fruit Forum

Many growers use the 5-1-1 Mix (5 parts 1/4" pine bark, 1 part peat moss and 1 part perlite. Also many growers use a 50:50 mix of Turface MVP and  Miracle Grow Garden Soil. Both are good draining mediums.  For 1/4" pine bark you can  use  Reptibark reptile bedding found on line or at  most larger Pet Supply Stores.

I go along with Poncirusguy,  my NZL fruit are mildly sweet and very mildly sour.

I have been using 5-1-1 medium for a long time.  It is a good medium. About a year ago I potted a tree in 50:50 mix of Turface MVP, and peat and I totally agree with Citradia, it is an outstanding medium.  Going forward as I repot my trees, all will be switched over to the 50/50 Turface/Miracle Grow Garden Soil mix.

I attended two Southeastern Citrus Expositions taste testing contest for the best tasting citrus. Both of the contest named Xie Shan Satsuma as the best tasting citrus.  This was  done by the vote of all the attendees at each Exposition.

If fine indoors , but curled damaged leaves when out on the balcony it is almost certainly caused by thrips sucking out the juices from the leaves.  Thrips damage normally is on new young growth, and not so much of firm mature leaves.  You can kill the thrips by a horticultural oil spray, or ever a soapy water spray.  Spray both to upper and lower portion of the leaf.  To avoid the damage, you should spray all new growth every 3 or 4 days until he leaves firm up.

It looks exactly like citrus mite damage.  The previous owner must have never sprayed the tree to eliminate the mites, so they just kept sucking out all the chlorophyll from the leaves. This is the worst mite damage I have ever seen.  To insure that the mites are either dead or gone, spray the leaves with a horticultural oil, or neem oil, or even two or three soapy waters sprays.  Never spray a citrus tree during the heat of the day.
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Your tree has all the symptoms of a magnesium deficiency.  Apply Epsom Salts (Magnesium Sulfate) at 4 Oz./gallon of WARM water as a foliar spray to the top and bottom of the leaves.  Do not apply during high temperatures or low humility.  Apply in the morning or late afternoon.

Here is some additional information taken from the internet:  Magnesium deficiency has been a major problem in citrus production.  Mg deficiency is commonly referred to as “bronzing.” Trees with inadequate Mg may have no symptoms in the spring growth flush, but leaf symptoms develop as the leaves age and the fruit expand and mature in the summer and fall.

I have  four of the kumquat varieties, marumi, meiwa, nagami and fukushu.  They all seem to produce about the same .

I'm sure you can get the tree from
Madison Citrus Nursery   https://madisoncitrusnursery.com/

Pagnr, gave you good information.  I use a horticulture oil spray for both thrips, scale, mealy bugs, and aphids,  Works well.

HLB in Poland is unlikely.  However, the leaves do have the look of an HLB infection.

Possible nitrogen deficiency.  Symptom start out as yellow/orange veins with some green out on far side.