I have some Cabomba Green (Cabomba carolina) that I put in my 10-gal Hagan Fluval Edge aquarium 1.5 months ago (their standard 44 LED light). Until 4 days ago, they were doing GREAT. They grew so quickly, I had to cut them and replant the cuttings.

Now, they all appear to be dying. They are slowly turning darker green to brown (they used to be a really vibrant green). The leaves are folding up and some are falling off. The worse bunch of leaves appears to have a little web of algae on it too.

Most recent tank events:
(1) I did a 50% water change 2 weeks ago (using filtered water AND added water conditioner)
(2) About 1.5 weeks ago, I killed a bunch of snails (25+) that had come with the plants (these or others I got on the same shipment). When I killed the snails, I smashed them and then pulled out the bodies with a paper towel. However, about a week later, I noticed 6-8 very small (.5mm thick, 5-8mm long) white worms on the back glass. They slowly got bigger. From what I can tell, they might be planaria.

It was 2-3 days after I noticed the worms that my Babomba Green started dying. Any ideas?

Last night, I did another 50% water change (hoping to get rid of the worms and help the plants).

Aquarium details:
No fish, just 4-5 different types of plants, 2-5 stems each
water check showed
PH: 8.0 (pretty standard for me, can't seem to get it lower, probably same as it's been for months)
Ammonia: 0 ppm (checked 2 weeks ago and again 2 days ago)
Nitrite 0 ppm (same two checks)
Nitrate 5ppm 2 days ago; 2 weeks ago it was 40-80ppm which is why I did the 50% water change with gravel vac

I have CaribSea's "Eco-Complete Plant Substrate" in there. It's been there since October (when I opened the new bag). It's about 2 inches deep.
For extra CO2 I dose daily with small amounts of Flourish Excel.

Snail note: I'm not sure it matters, but the snails I killed off were small, mostly translucent, and moved in a continuous gliding fashion. I did not kill off my 3-4 trumpet snails (which inch around, moving more in steps than the other kind). I now have one big trumpet snail (1 to 1.5 inch long) and probably 6-8 smaller ones (some are just big enough to see).