If it's the meyer lemon or any other dwarf variety I'm pretty sure it doesn't need a second plant. I've read online that if left outside it'll get pollinated and if left inside it might even pollinate fine just from it's own pollen floating in the air if a fan is running; however it's recommended to take a cotton swab or paint brush or something and pollinate it yourself.

As for the salt question I'm curious about that too.

Typically the sign of salt build up, also knows as salt toxicity shows up as "burn" on the tips of leaves first. Normally it is fairly uniform, meaning new and older growth is effected the same. Just because you water with rain or snow melt will not mean you are forever free from salt buildup. What I and most others do when we water our container trees is allow about 10-20% runoff. This practice generally prevents salt buildup. However, by your description, it is possible your tree is lacking nitrogen - the yellow/green color is the indication. To be sure we will need a photo. The lemon will not need a second plant for pollination it will flower and fruit in time. Variegated Eureka is notoriously weak and non vigorous this tree will probably just take much more time then the much more vigorous calamondin (you have one of the slowest growing citrus right next to one of the fastest growing citrus, not good to compare) Again, post a photo more more feedback.

Either I am confused by what you mean or you're confused by what 'salts' mean. lolol

When we speak of flushing 'salts' from our containers, we do not mean salt as in table salt, sodium chloride. We are not speaking of road salt.

Soluble fertilizers are salts and improper watering can cause them to accumulate. Even our water can be a source of salts, such as sodium, calcium, and magnesium. Many potting mediums have a too high level of soluble salts and leaching a new batch before using it for planting is a good idea.

We really can't avoid using these fertilizer salts, but by adequate flushing of the soil system, we can certainly prevent damaging build up. Offering our plants little sips of water, never drenching the heck out of them, and feeling obligated to add 'something' each and every time you water can all create a build up of these salts.