Pothos dying?

[kimmcannally]

Anyone else using Golden Pothos in their tank?

I've got it in a 55 gallon with two 48" T8 bulbs (6500K), completely submerged.

It was doing great until I added API Leaf Zone and Seachem Flourish last week. Today (8 days later) I noticed that two of them are dead.

The third one is doing just fine, but it's in the top of an ornamental stump instead of being planted in the sand. I put an API root tab by the ones in the sand and left the other one alone. Think the root tabs did it?

The dead ones are also on the filter side of the tank, so get more water agitation. I left the roots in the tank, as the part that is left is still firm and has roots growing out of it. But most of the stems and the leaves just turned to mush.
If the other one (which has been in the tank longer) wasn't doing so well, I'd think they just can't grow submerged in this tank. But the first one is doing fine.
Any ideas?
Ammonia 0, Nitrite 0 Nitrate was up to 40 (WC now) and pH 7.0

In this same tank I have Frogbit, a couple of Java Moss "sheets" growing between plastic canvas for now, an Amazon Sword, a Crypt, an African Water fern and an Aisian Water Fern and a couple of Anubias - all are doing fine.

Added some pics of what I've got. Lights are on 7 am to 9 pm with an hour break (just changed that to a two hour break since I have some algae now).
You can see the Pothos that is doing well and the root system left of the one that melted.

 

[Rivercats]

I have a huge Pothos hanging on the 220g with roots and stem bottoms in the water and leaves hanging over the side. It's a year old and I have to cut roots in the water back every few months since they grow almost 30" down to the substrate and the outer leaves/stems need trimming also. It's not an aquatic and over time will die. Adding the nutrients has nothing to do with them dying. I use high doses of liquid carbon and fertilizers daily which seems to only add to growth.

 

[kimmcannally]

Huh. I had read they can live submerged for extended periods of time, and these have only been in the tank for a couple of weeks! The one that is doing well has been in for about a month or a little longer.

I've got some in my AC 70's too and love it. Think the "dead" ones will grow back from those roots I left in, or should I just toss them?

Also, I got the Flourish and Leaf Zone from your advice, thank you and I'm only dosing 1/2 dose or a little less since I have so few plants in the tank right now. This is the correct thing to do, right?

 

[Rivercats]

I would remove the roots as I really don't think any new growth will form. I've actually never read the entire plant can survive for long periods underwater but know that roots can grow indefinitely in water without every being planted.

As for the ferts as long as your plants are doing well and not showing any signs of nutrient deficiencies I wouldn't change the way your dosing.