Just a short note, tonight Spawn #24 was pulled for hatching.  I set it up with 100% new water, at 1.025, with aeration provided by a limewood airstone and a hatching escape route set up at the top of the tile.  The bottom of the tile is held in position by another tile lying on the bottom, and at the far end of the tank a small white LED nightlight is on to draw larvae  away from heavy flow.
Wish us luck!