Java Fern is one of those plants that will is 'Har to Kill' It will grow in almost any conditions.
The Riccia on the other hand will grower than I said as I didn't realise you didn't have CO2 (This will also mean it won't pearl)
Why not DIY yourself a CO2 bottle up and then buy a diffusor of some sort like the Nano ones from Aquatic Magic (They are about $10)
http
/cgi.ebay.co.uk/Nano-Co2-diffuser-Sm...1QQcmdZViewItem
My DIY bottle (I also have 2 Nutrafins) is just the following:
1 x 2 Ltr Coke Bottle
1 x CO2 hose straight connector Join (1 pack of various hose connectors = $2 from your local DIY shop or LFS)
Silicone Sealant
Put 1 hole in the centre of the coke bottle lid with a bradawl (or sharp spike) making sure the hole is smaller than the hose connector)
Widen the hole both sides with a philips screwdriver
Push the hose connector into the hole (This needs to be tight)
Seal bothe sides with silicon sealant (Aquarium type)
Leave 48 hours to cure properly
Attach Co2 or airline tubing (CO2 tubing is much better as it lets less escape and is approx $3 on ebay)
Attach to the diffusor in the tank
Mix for the bottle:
11 desertspoons sugar
1 teaspoon bread yeast.
Fill bottle with warm water to ½cm above where the bottle starts to curve towards the lid
Screw the cap on tight
Wait 2-3 hours for it to start working
There is also a recipe on the diffosor link above if you want to use a bigger bottle
Viola CO2
Change mix once a week in your lights out period
Andy