I guess you have found that Riccia doesn't like gluteraldehyde. I don't think I have ever overdosed a tank with Excel to see if it has the same effect on the Riccia. Looks like you may need to experiemtn with some Excel in the tanks for a few days
Gluteraldehyde may be a good idea for those looking to eradicate Riccia from their tanks assuming it does no harm to any of the other plants in your tank!