I have now added a couple of real plants to tank number 3.

First is a Bacopa monnieri


and secondly, a couple of Echinodorus bleheri (the one in the background - below)



These two were 'borrowed' from the livebearer tank, where they have flourished for about 2 months. They have now lasted about 6 hours in this tank, so things are looking up.

Will report back later.