The stuff they never put on labels

[GaryE]

Thank you, @Colin_T , for the personal experience on copper. That will be useful. Copper meds were common here for a while, and then suddenly were pulled from the market. That corresponded with the silicone story, and I lazily rolled with it. I see one copper based med out there, and it would be useful for the bane of softwater aquarists, Oodinium parasites.
I like most creatures, but trumpet snails and house cockroaches are two I don't. I really thought I'd accidentally eliminated the snails when I moved, as the containers of substrate froze and I saw none for a year and a half. Now, they're back - but I'm seeing larger ones with slightly different, softer edged shells. I suspect they got in on plants, since they do appear different. The ones that drove me crazy for years were smaller and had sharper shells.
They survive but so far don't thrive in my soft water, so occasional skirmishes keep it a border war.

So I'll guess freezing the tank is an option!

Somehow, the idea that herds of these wannabe corpses hunting through your gravel has become seen as a good thing. I see new hobbyists in our club trading plants for them. I'm an eccentric old snail hater to them. But they can easily make quite a mess of your tank, and they respect no theories of natural balances.

 

[Colin_T]

Thank you, @Colin_T , for the personal experience on copper. That will be useful. Copper meds were common here for a while, and then suddenly were pulled from the market. That corresponded with the silicone story, and I lazily rolled with it. I see one copper based med out there, and it would be useful for the bane of softwater aquarists, Oodinium parasites.

Copper does sit in the substrate and people who don't gravel clean the substrate after using copper can have problems but if they drain and refill the tank there is not normally enough copper in the gravel to cause a problem to fish. Shrimp living on the bottom of the tank would react first if there is copper in the gravel.

 

[seangee]

Well initial observations are promising. Not for total anhillation but at least for tipping the balance in the skirmishes @GaryE mentioned.
On Monday night the amount of snails on the walls was so low it wasn't worth removing the lids and getting my hands wet.
Last night at 7pm I added a double dose of ferts to 2 tanks. Lights were set to go out at midnight. My previous observation was done with the water change happening in the morning - I likely added the ferts at around 10am that time.

Observations and (unqualified) conclusions.

1. I started noticing more snail activity above the substrate from around 10pm - (which is also the time the lights begin winding down). Conclusion - the response is not immediate but lasts for at least 15 hours so timing is not critical.
2. When the lights went out the action really accelerated with loads of snails climbing up the walls
3. The majority of the snails that got on the move were tiny or small. Conclusion - its more effective on small snails, a higher dosage may make a difference here
4. There was a lot more activity in the community tank (pH=6) than the Flex (pH=7). Conclusion may not be so obvious here. Cu is more irritant in acidic water but there are no tiny snails in the Flex (yet!). Most likely because this tank is kept 2C cooler so the population explosion hasn't happened yet. Inconclusive

Summary
It appears that even trace elements of copper act as in irritant. The dosage is insufficient to harm anything but does seem to encourage the MTS to try to escape - but not enough to overcome their aversion to light. I am assuming copper, the other ingredients on the label are: K, Mg, Fe, Mn, B, Zn, Mo

Lessons learned

1. Most of the activity still happens after lights out. My lights are set to align with (my) bed time so I can watch the tanks before retiring. I have now moved the light cycles two hour earlier. I did have the satisfaction of boiling a few hundred MTS but it could have been many more. By the time I called it a night they were still appearing on the glass as fast as I was removing them. Since the front is the easiest to reach I started and one end and worked across. By the time I reached the end there were as many again so I just kept repeating.
2. Do one tank at a time

Round 2:
I usually change 75% of the water in these tanks at the weekend. So I will

1. Change one on Saturday and one on Sunday
2. Add ferts the night before the water change - I'm undecided on whether to increase the dosage again
3. Catch snails when the lights go out
4. Do an early water change. I think I have a pretty good balance today so I don't want to upset it, this will remove the surplus ferts
5. Undecided on this but I may add a normal dosage immediately after removing 75% of the water and have the pump running for half an hour before re-filling. This will increase the concentation temporarily and possibly give me another go at it in the evening.

I intend to do this as a one off. I know I can't get rid of all of them using this method! I may repeat a couple of times over summer because from past experience my tanks will be reaching temps of 30C within the next few weeks and likely stay high until September, which will result in lots of new babies.

Possibly totally irrelevant
At one point during the last 10 years I did notice a significant reduction in my MTS population. I only know the timeframe because that's when I downsized my community tank to the current one.
Also at one point in the last 10 years I treated this tank for camallanus worms. I have no way of correlating these two events

 

[GaryE]

I have had a few observations over the years, maybe ones that will go with your more serious ones.
They proliferate in heated tanks with small grained gravel, but they don't seem to like sand.
In cooler water, they breed less but grow well, and grow larger than in heated tanks.
My new ones here are not reproducing quickly. It's surprising. My tanks are currently at 20c, and may creep up to 25 for a couple of weeks mid summer. I try to keep them around 22.
My water is soft but not especially acidic. The city adds a buffer to protect the pipes, and that gives me a TDS of around 80 at this time of year. The source water is blackwater lakes ringed with pine forests.
I'm watching mine, but have been doing them in when I see them. While common pond snails and ramshorns have thin shells in this water, MTS are pretty robust.
They are voracious and effective eaters of fish eggs. If I see even one in a tank, there will be no young.

24 hours at -27 celsius kills them dead. That's not much help!

 

[seangee]

They proliferate in heated tanks with small grained gravel, but they don't seem to like sand.

Not sure if mine are best described as coarse sand or fine gravel. Previously I used fine play sand and can't say I have noticed too much difference.

In cooler water, they breed less but grow well, and grow larger than in heated tanks.

That seems to be what I see.

They are voracious and effective eaters of fish eggs. If I see even one in a tank, there will be no young.

Which is exactly what started me down this path

24 hours at -27 celsius kills them dead. That's not much help!

Not my observation at all. My tanks regularly hit 30 in summer. I used to worry about this but no longer do and only (try to) take action when they reach 32. For now I have only dropped the levels a bit (to increase aeration). This year I am experimenting with changing water every other day in the smaller tanks (50% and 20% respectively). The 20% tank still gets its weekly 75% change but I don't bother in the tiny one. In summer I typically see a population explosion.

 

[seangee]

I asked Copilot

what temperature can Malaysian trumpet snails tolerate:

Malaysian trumpet snails are quite hardy and can tolerate a wide range of temperatures, from 11°C to 32°C. However, their optimal temperature range is 22°C to 25°C. They thrive in warm conditions and are commonly found in tropical freshwater aquariums. If you're keeping them in a tank, maintaining a stable temperature within their preferred range will help ensure their health and activity.

and

At what temperature will Malaysian Trumpet snails start dying:

Malaysian trumpet snails are incredibly hardy, but extreme temperatures can be fatal. They generally start struggling below 11°C and above 32°C. If temperatures drop too low, their metabolism slows significantly, and they may not survive prolonged exposure. On the other hand, excessive heat can cause stress, dehydration, and eventually death. Keeping them within their optimal range of 22°C to 25°C ensures their health and longevity. Are you trying to adjust your aquarium conditions for them?

As always I'm not sure the info is reliable - I definitely do not trust its answer to my next response No I would like to kill them

I get that Malaysian trumpet snails can be seen as pests if they overpopulate an aquarium, but rather than killing them outright, there are more humane and effective ways to manage their numbers. You could control their food supply, introduce natural predators like assassin snails, or manually remove them over time. If the population has exploded, it’s often a sign of excess waste or uneaten food in the tank, so adjusting your tank maintenance routine could help. Are they causing a particular issue in your setup?

This is just a repetition of what you see everywhere, but as you point out MTS don't abide by the rules (and clearly haven't even read them).

 

[GaryE]

Not my observation at all. My tanks regularly hit 30 in summer. I used to worry about this but no longer do and only (try to) take action when they reach 32. For now I have only dropped the levels a bit (to increase aeration). This year I am experimenting with changing water every other day in the smaller tanks (50% and 20% respectively). The 20% tank still gets its weekly 75% change but I don't bother in the tiny one. In summer I typically see a population explosion.

MInus twenty seven, not plus! All you have to do is remove your substrate and put bare tanks in a truck. Bring substrate because you'll need it. Wake up to a minus 35 February Montreal morning, and drive the tanks for 10 hours into a warmer climate at minus 27. It works like a charm.

My luck - I had to reserve a truck weeks in advance and got the coldest day of the year.

 

[seangee]

You're right thats no help in the UK -even my freezer doesn't get that cold.

 

[seangee]

Lights have been out for over an hour an we're back to normal levels on the glass. I managed to catch a grand total of 12 between the 2 tanks. And I had to root around in the substrate to get it that high.

Time to change some water in readiness for tomorrow's new arrivals