I can't comment on the relative merits of these tanks so I'll leave this to someone else.
Although 'footprint' (i.e. length/width and depth) of tank is an important aspect - always good to get the largest footprint you can accommodate as that will increase your options for fish - one aspect to consider with these tall tanks might be the ultimate height and whether you can reach the various corners for tank maintenance purposes. I know of several people who find their short height has been problematic for the Juwel Lido. The Aqua One 110 looks similarly tall, though. It would be worth establishing the overall height once you take into account the tank and the unit it will be placed on (whether the one designed to accompany the tank or a separate one), unless you are tall and this aspect would be of little consequence.
Another aspect worth considering might be the lid, especially if you would be relying on an auto-feeder at any stage. I had a wonderful lid on my old tank which accommodated a Fishmate Auto-feeder perfectly inside, on an in-built heavy-duty condensation tray with feeding hole, from which I could feed the fish if away. I didn't appreciate how important this was at the time. My newer tank doesn't have this feature, and, to use any auto-feeder would either require the lid kept open or a condensation tray with feeder hole cut into it - but the gap(s) would result in my nerite snails escaping or potentially fish leaping out.
The filter media in the new/temporary tank would need to be cycled, otherwise there is the possibility that the fish will be experiencing the effects of ammonia. To do this (if you haven't already), all you would need to do is move a small portion of the filter media from the main tank's filter into the new tank's filter. In essence, the main tank's filter will have enough filter media to process the waste of its inhabitants, so, if you move across roughly the appropriate percentage of that filter media for the two pregnant guppies, that should suffice (e.g. if there are 8 guppies altogether including the 2 pregnant ones, then move across ~25% of the filter media into the new tank's filter).
Is the filter outflow particularly strong .v. the size of the tank? I've had fish hide by the filter due to being buffeted about by a strong outflow, and have addressed this by either turning down the flow or putting a small piece of filter media over the outflow nozzle to reduce the strong output.
As you have rocks/plants and potential hiding places for them, I can't think of any other particular reason for their behaviour, other than possibly wondering where their tankmates are (but I do think you've done the correct move by moving them across to give birth in peace) or possibly nervousness about the impending births.
I'll admit I'm perplexed here too - there is nothing from what you've described that is ringing alarm bells for me. [I'm assuming it's ammonia/NH3 and nitrite/NO2 that you've provided results for, and that your nitrate/NO3 isn't higher than 20ppm above your tap water nitrate levels.] I'll keep having a think but hope that's of some tiny consolation in the interim. I just hope I - or someone else - will be able to come up with a more helpful suggestion to prevent any further fatalities, though...
I wonder if an interim measure might be: * to do a small daily water change of say ~10%. Rather than a full substrate-siphoning water change, the simple removal of a few jugfuls of water and replacement with dechlorinated water daily might help dilute anything that may be present in the water that isn't detectable via home-testing kits such as fishes' stress hormones which may be being released given the current situation (whatever it is); * to do a quick internet search to check if your water/utility website has mentioned any particular treatment works taking place recently that might account for this.
Fingers crossed that I or someone else may be able to suggest something else in due course...
Sorry to read about this and I know you'll be hoping for an immediate solution rather than more questions but it would really help us a lot to try to figure out the problem if you can let us know: * actual test results for ammonia, nitrite, nitrate and PH * brand of test kit(s) * what brand of filter you have and what type of filter media is in it, plus what your maintenance regime is on it * how regular the 20% water changes are * what your water hardness is in CaCO3 (PPM) and/or German degrees hardness (DH) * how long the tank has been established, and roughly how long each of the inhabitants have been in there * is there anything that coincided with the onset of the spate of deaths, such as an external toxicant like a plug-in air freshener? [https://www.practicalfishkeeping.co.uk ... -that-can-kill-your-fish/] * have you ever noticed any of the fish bullying (or, conversely, others cowering/hiding)? [How often is the fishtank in your line of vision to be able to gauge whether this might be going on by one/several fish?]
Sorry to read about your losses - on the basis of my experience so far, I would say that the worst fish deaths to experience are those involving fatal accidents... and in/behind the filter is often a location for such to occur despite any gaps seeming impossible for them to get in/behind. Filter wool is often useful for squeezing into tiny gaps like this. Your advice will hopefully be very helpful for anyone else with this model of tank, to alert them to its filter's potential dangers - thanks for highlighting this.
In terms of "doing everything right", the perils of the internet are that it is difficult to know that all has been accounted for and to distinguish good from poor sources (although fishkeeping.co.uk and other UK-based forums are reliable sources as they contain key articles such as at https://www.fishkeeping.co.uk/beginners_articles/, supplemented with Fishbase and Seriously Fish).
Hopefully you have done a full fishless cycle https://www.fishkeeping.co.uk/articles ... hless-cycling-article.htm before adding any fish, in which case ongoing water quality monitoring (and addressing accordingly) ought to ensure the remaining fishes' health as best as possible (in addition to having reduced the possibility of fatal accidents as you've experienced). HOWEVER, one aspect I would point out is that the 60-litre BiOrb, whether the Classic or Life model, does not have the 'footprint' required for white cloud mountain minnows (or indeed any fish really other than possibly a single male betta / Siamese fighter fish). www.seriouslyfish.com is an up-to-date source for minimum-sized tank requirements, and the mimimum 'footprint' (i.e. distance throughout the tank, not just at the widest part as per a Bi-Orb's round shape) requried for WCMMs is 60cm x 30cm. The tank would be ideal for shrimp, snails or aquatic plants, though. :)
If you still think it's worms, rather than poo, than you'll absolutely have to get video footage of these worms when moving about *with any filter current switched off* and also of everything you're describing on the fish themselves and the fish behaviour generally - without that, it's likely that any vet (in the UK or the USA via justanswer.com) will reach the same diagnosis as Fishlady (who is extremely experienced). No, the USA vets on justanswer.com will not prescribe medication but may or may not suggest contacting an aquatic vet here in the UK if they think the situation requires it.
I think that, rather than getting the professional advice it sounded like you were going to get, you've been "palmed off" to a standard member of staff - an aquarist is someone who keeps an aquarium, so they could have any level of experience and may only be basing their response on their own experience, but I think you've summed up the likely situation very well. Anyway, it's clear from everything you've said that we know what we're dealing with, so I would ignore that side of things and work out a way forward between us.
Just to check - presumably you didn't have any carbon in the filter when you dosed the medication? (If so, that prevents it working properly.) What is the standard course of medication, how many days did you dose for, and does it mention extending the treatment course?
Are you able to take a video of the fish and the worms, and upload the videos onto YouTube? That would be worth having as evidence for anyone you seek advice from. If you're really keen for a veterinary opinion, then you could use a service I used in the past before I was aware of these forums' existence - I sought advice from vet professionals with aquatic expertise via www.justanswers.com in the USA; from recollection, it was about £25 for basic-level advice and there were 3 tiers of advice but even the basic level was well worth it for peace of mind. Alternatively, one of the aquatic vets via the link I gave you the other day may be able to help, or local unis' veterinary depts (if there's one near you) may have folk who specialise in fish and be very willing to help.