i too had that problem! and still do after 2weeks i also have the spiral val that grows really fast (like an inch a day) and it just breaks and falls apart mid leafish.
So a week ago i added a co2 diffuser and another day glow light and they are still dying and i still cant figuer out why!
I have a 4ftx1.5ftx1.5ft with 2 day glows and 1 co2 diffuser. in it i have java fern thats donig really well, cabomba doing well, baby tears, brizilian sword both donig well and both the vals are dying. so hmmmm cant figuer out what the problem is