Reusing soil?

Do people reuse their soil indoors? My soil right now seems to be very "active", if a leaf drops I can see how the soil creates a white kind of fungus and starts decomposing the leaf. However I am getting less yield every time I reuse the soil. I use biobizz light mix and use biobizz nutes. Is it possible there might be salt buildup, or shall I just get new soil every grow?

If you add amendments suited for flower, then straight away use that soil for germination/veg it's possible the NPK balance is out a bit. What i done is use fresh soil for germination in solo cups and all the soil from the previous grow added EWC and some veg specific amendments and let it cook in totes for 2 weeks. Second grow the soil was much better than the first.

i use the old soil for potatoes, they turn soil back to useable sooi somehow.
ill use part old soil part new, i have found that you get defiscancies if you use amended used soil. this leads to plants that show problems early on in growth, untill the amendments kick it, in particular, too much phosphrous by the looks of the leaves..
if you get a soil testing kit. im sure you can add amendments and bring the soil back to near perfect. but ive never let the soil cook, thats something to try this year

My mix for our favorites is 60% reused, adding some meals, mostly replacing castings, composts and peat moss. Been doing it for years.