Riccia is not the most sensitive plant to Gluteraldehyde, but it does have its limits.
I found I could dose 1.5ml of Flourish Excel per day to a 20litre tank with no ill effects to the Riccia (although i was changing 50% of the water each day).
I don't know if Easy carbo and Excel have the same concentration of Gluteraldehyde, but look out for the riccia tips turning white. If this happens you are definately overdosing too much.
Cheers,
James