Did you have CO2 running? I believe hygrophilias do much better with CO2. I have found almost all my plants (pennywort, water wisteria, etc) will develop pin holes and die except ones in the tank with a huge collection of humus and mulm/little water changes/mostly distilled water since decaying things give off more co2. You could try any number of these. Humus also gives off a lot of ammonia, which is not good for fish, so upping co2 or adding might be better.