Mass plant die-off

[whomeverwiz]

I have a 29 gallon in my office with a bunch of buce and crypts. It's home to a dozen neocaridinas, a dozen green neon tetras, and a pair of apisto agassizii. There are a couple tiny java ferns and a bit of moss as well. I use CO2 on a timer. Everything has been copacetic for about 6 months or so.

I did an 80% water change last week, and stuck a few more buce/crypts and some dwarf hairgrass in there. The pH came down a bit as expected, and the water turned a bit cloudy, what looked like a bacterial bloom. I left for the weekend, and when I got back to work all of the new buce was almost gone, all of the crypts, new and old had melted, and even my old well-established buce looks like it's disintegrating. All of the shrimp and fish look fine. Also... the java fern, hairgrass, and moss look totally normal.

I fertilized a touch after the change, but I'm at Nitrates 20, Nitrites 0, Hardness 75, Buffer around 100, pH 7, no chlorine. 

Did I get some round-up in my tank? Not sure how I would, but there is some sitting outside my building near the hose that I use to fill my water bottles and I always give it a side-eye when I go out there. Because my non-dicot plants are fine, I'm really suspicious of glyphosphate. Also just super-sad about the devastation of my plants that I loved so much.

If somehow I did poison my tank, I'm terrified. I know that bottle of round-up is out there, but I never touched it at all! I think I can never use that hose again anyway.

[PaigeIs]

It's likely that the large water change is the culprit.  Plants don't like big swings in water parameters; some are more sensitive than others.  Both crypts and anubias are low-light plants so it's doubtful a couple of days of cloudy water caused a melt, but maybe?  Regarding the Round-up. It's hard to imagine it would impact the plants so severely but not impact the shrimp. Also, what are your water parameters?  Not all plants like the same environment.  It's worth comparing what the plant, by type, wants and what your aquarium delivers. The issue is more likely a big water change.  It's hard to watch plants "die," but if you are patient, they will most likely rebound just fine.  Keep in mind slow-growing plants require patience.

Anyway.. here is a good article from Aquarium Co-op about why plants melt.

https://www.aquariumcoop.com/blogs/faqs/melting-or-dying-plants#:~:text=It is normal for plants,to start taking in nutrients.

[whomeverwiz]

No anubias, just buce... I've done big water changes like this and never had anything like that happen. I know crypts are sensitive, but I've never had a buce die on me at all, much less melt in a couple of days. 

Anubias? Well, they die on me, but it's the rot that does it. Never had them melt.

As far as round-up toxicity goes, you can kill shrimp with it, apparently, but dicotyledons are sensitive at much, much lower doses. The pattern of which organisms died is mostly what you would expect with glyphosphate poisoning. It is considered "slightly toxic to practically non-toxic" to aquatic invertebrates. It doesn't kill moss. Apparently it kills the rhizome of ferns and prevents reproduction, but doesn't kill the vegetative growth of the fern. The dwarf hairgrass seems like it should be susceptible, though, and it didn't seem to suffer much.

Are there other water parameters you would like to know aside from the ones I posted above? My tap typically is from 20-40 TDS with no detectable chlorine (and is no different today), but I know there is chlorine in there, so I still treat, of course. I keep the tank at 76, and it dropped to about 72 with the water change, and I've done that several times before and never had a problem with that. pH went down to about 6.8, also not unexpected.

I know a big water change can cause issues, but it never has for me before. I can't convince myself to chalk it up to the water change just yet.