OK, so here's what we did. I'm just a beginner, but these are things that have worked well for us so far.
--- Too high in acid
The farm smelt 'sour' to me. This has been mentioned as a BadThing. ie: if castings have been there too long, sometimes they will be too acidic.
* solution: add dolomite. I threw a good handful in for good measure and stirred well. Apparently, leeches hate dolomite too.
* More research indicates eggshells will also keep acid levels down. We don't put onions, garlic or citrus in, but it's worth mentioning they're very acidic and should be avoided.
* I'm also planning to cycle the castings more often.
--- Pick out leeches
* During stirring process of all layers, I carefully picked out twenty leeches. This is an ugly process, and I wear decent, thick, waterproof gloves. Leeches are hideous things. Some people talk of throwing them in a bucket of dolomite, but at first I just put them in plastic in the freezer so they died more humanely. I don't bother anymore.
--- Farm is too wet
* Dry out the farm - leave lid off on a warm day so they go to the bottom of the tray and scrape as many castings from the top layer as possible. Remove any shelves beneath and rest the affected tray on the liquid level only.
* As the affected tray was then rather low, I actually watered this down to try and flush through some of the castings and the acid content. This might not be the best approach, but the acid concerned me. I left this tray at the bottom with no castings touching the floor above. I scraped channels in between to aid water flow. Added other trays back on top so the acids didn't go back into the food.
* Finally added sandy, dry soil. This balanced up the mix and aids worm digestion anyway. In a few days, the trays smelt much more earthy and fresh. This seemed to be one of the most important parts of the process.
--- After another week, I stirred and checked all layers, finding only 3 leeches that were put in the dolomite bucket.
--- This takes some time
It is also worth mentioning - i don't have children or pets. While I find the worms a little hard of hearing and somewhat difficult to train, I am very fond of the creatures and pay close attention to their needs. If I had a lot less time, I'd probably just throw soil and dolomite in there, and hope for the best.
