What kind of filtered water? If I go only by odds and reasoning, the first thing that comes to mind is that you are over-nurturing - which translates to over-watering, even though you say this is not an issue. Salt accumulation in the soil (from fertilizers and irrigation water) is another strong possibility, as is natural abscission (losing leaves) due to a reduction in already low light levels. The moisture meter doesn't work. It measures electrical conductivity - not actual moisture content, so it's actually closer to reliable as an indicator of fertility levels than of moisture levels, although it's really not a reliable tool for measuring either. Test your plants by checking the soil at the drain hole & only water when it feels dry there. Al

Normal potting mix for a succulent generally retains too much moisture, and 50% coarse sand helps but probably does not tip the balance. If you do not want to hassle with creating your own mix from scratch, I would change the soil to 50% commercial "cactus mix" and 50% perlite. I prefer pumice to perlite since it is heavier and does not float. Since you have your own greenhouse, I am wondering do you have a lot of succulents, and are most of those in the same soil and thriving? Is there any chance the greenhouse becomes extremely humid or hot?

tomatoes are not really house plants... and it wont be easy trying to make them such ... so there could be a myriad of issues making the plants weak ... allowing for an infestation of other problems ... if they were outside .. how did you 'clean' them.. before you brought them in ... in case there is another try next year ... have you isolated them yet??? ... you dont really want to spread this to all your houseplants ... how do you plan on caring for these absolute full sun plants indoors all winter??? ..lights.. humidity ... outgrowing the small pots they are in .. etc ... im sure there is something there.. but im not convinced you can 'see' a spider mite.. in a pic ... or im wrong.. whatever ... lol it will be a fun experiment.. and you will learn something for sure ... but dont get upset.. if you fail .... the learning is for next time ... ken

Was recently shopping in nursery in Ontario (not a box store). They had a truckload of large citrus trees that just arrived from Florida. They were $399 and $799 for 10 and 20 gallon trees. Unfortunately they were covered in red citrus mites. They were easy to spot. I took a magnified picture of the mites with my iPhone and showed the owner. He said they just arrived from Florida and they had not got around to spraying them for mites yet. In theory they should have been sprayed in Florida already for mites but that is not always the case. The first two pictures of a lemon tree could show salt build up or sunburn. Third picture shows a sticky honeydew substance on the leaf. This is a signal that something is piercing or sucking the leaf. Could be scale or spider mites. Look on the underside of leaves. Spider mites you might see with naked eye but easier to see with a magnifying glass. Mealy bugs are easy to spot. Regarding the shape, it could be mechanical damage. When the leave grows it will grow around the damaged which distorts the shape. Overall your trees look in pretty good shape. The low humidity indoors is extremely hard. Moving them outdoors in the spring will help. Spider mites thrive in low humidity. Mealy bugs thrive in high humidity. Skylight won't be enough year round. They will need to go outdoors and you will need a grow tent with LED or something else for 8 months. A typical skylight will help but not enough light to sustain the plant.