I have a terrarium, now 48 years old. It is in a large bottle approx. 100cm (or 40 inches) in circumference and 50cm (20in) high. the top opening is about 15cm (6in) wide with a cork closure. Over the years I have occasionally, maybe every 2nd or 3rd year, cleaned (with well rinsed clean disposable towel) the inside glass, wiping away green stuff (??) and sometimes adding half a cup of filtered water. It originally had maybe 3 plant varieties, over time one has taken over and I removed the other dead ones. I must have been doing something right for it to last so long but lately it's looking quite unwell and the soil is looking black and soggy and the remaining plant has gone from looking quite healthy to looking straggly though the leaves are still healthy. There is quite a layer of dead roots on top of the soil. The original cork closure shrank over its 48 years and for some time I stuffed layers of plastic film around it to keep it air tight until I found a new, well fitting cork lid. I would appreciate some advice on what to do with it now to get it back to its former glory.