There is a great deal of variation between and even within local fish/aquarium shops - some staff are trained to sell products and mainly those which their particular shop stocks and to sound knowledgeable and convincing in order to make sales, other staff have a varying range and breadth of expertise (some with little experience and others with many years of experience but very stuck in their ways and who haven't evolved with time or embraced new developments). For that reason, I'd exercise a word of caution if hoping that speaking to someone in a local shop will provide you with all the answers you need.

Generally, Eheim and Fluval have a solid and excellent reputation, so filters or tanks or any products from either of them will be good. Juwel tanks also have a good reputation.

If you are upgrading the filter, then do make sure that you don't subject the fish to an unnecessary fish-in cycle - make sure you transfer all of the existing filter media into the new filter just before switching it on for the first time to ensure that it's instantly cycled (or, if running both the old and new filters, put some of the media from the old filter in the new filter to ensure that the beneficial bacteria 'seed' the new filter).

I'm not familiar with London and its local fish/aquatic shops (LFSs) but have read of some which have a good reputation including an area which has a large concentration of LFSs within the vicinity (about 5 within 1 square mile or similar!) - I'll try to unearth the information and post it on here if/once I find it but Crew's Hill rings a bell as the name of the area. The latest edition of Practical Fishkeeping magazine mentions The Aquatic Design Centre in London and Maidenhead Aquatics at Morden as topping their readers' poll for the London area for last year.

[Edited to add: my memory was correct. Wildwoods (https://worldofwater.com/hertfordshire-enfield/) is the name of one of the LFSs, and apparently there are a lot of others in the area. After a quick google search, I've found Ocean Marine Aquatics, Kingfisher Aquatics, and a few branches of Maidenhead Aquatics such as Enfield, and a Crew's Hill Pet Shop - wow, spoilt for choice if you go to that area! A bit further north, there's also ND Aquatics who make custom-made aquariums.]

Guppies' requirements are for a range of 143-536 ppm, so your water is within range (GH of 10 converts to 178.5) albeit on the lower side of that. [My apologies for forgetting that you lived in Israel and not the UK in my earlier post.]

The guppy with the raised scales sounds as though it might have been dropsy - was the whole body covered in raised scales or just a section? If the fish become bloated and especially if their scales raise which suggest it might be dropsy, then giving them Epsom salt / magnesium sulphate baths can sometimes help. However, if you think there might be a bacterial infection causing the bloat problems and the dropsy, then quarantining the affected ones to treat for bacterial infections might be best.

Yes, it seems that what has happened is that, between you cycled the tank (or, more accurately and best to think of it as, cycling the filter) and then actually put fish in the tank, the beneficial bacteria built up during the cycling process went dormant and then died, so you're now doing a fish-in cycle. [This article helps explain the fishless cycling process well: https://www.fishkeeping.co.uk/articles ... hless-cycling-article.htm.]

What you ought to have done between finishing the fishless cycling process and introducing the fish was to continue dosing with ammonia as per instruction no.6, and then done a large water change to reduce nitrates just before moving the fish into it. Alternatively, the newer tank would actually have been instantly cycled by moving all of the filter media out of the former tank's filter and into the newer tank's filter at the same time as moving the fish.

The best way to address the problem you now have and reduce the ammonia and nitrates level (and keep nitrite at zero), now that the fish are in it, is here: https://www.fishkeeping.co.uk/articles ... ammonia-nitrite-spike.htm

On a separate note, keep an eye on the endlers and the betta(s) (fighting fish) - often bettas try to fight with fish which have flowing tails like their own. If you've had them all for 2 years without issue, then hopefully they'll be fine, but, if not, keep an eye on them and be prepared for a back-up plan such as a new/separate tank for the betta(s) if problems arise.

If you live in the UK, try inputting your postcode into your water company's website to find out the water hardness level in CaCO3 or German degrees hardness; that ought to give us an idea, even if you don't have a test kit just now.

Are you feeding them currently? If you do feed them during winter, then it's worth at least cutting back on the amount of food as the fish go into hibernation mode and their metabolism slows down - it may be that the food is not being properly digested and is affecting the swimbladder. If you do feed them, then I'd suggest, as well as cutting down on the food, interspersing flake/dried food with some peas with the shell off - that might help.

Let us know if this works or not and, if not, we'll try to advise further.

Same to you all too. :)

The only other suggestion I can think of, and I don't want to raise your hopes, but I vividly recall at least one person on another now-defunct forum who swore by Repashy Soilent Green for swimbladder problems in goldfish. Although the formula is/was not created for goldfish, she did have success with it - spirulina is an ingredient in it which is meant to be beneficial for swimbladder problems. If it's not too late, I wonder if that might be worth a try.

The evidence is generally patchy on the effectiveness of these products - fishless cycling https://www.fishkeeping.co.uk/articles ... hless-cycling-article.htm is a more reliable method of ensuring the tank is fully cycled, as well as being much more ethical.

If using these products, then Tetra Safestart and Dr Tim's One and Only products each use the same recipe and have the correct species of nitrite eater required; however, their effectiveness if very much dependent on ensuring that the products are kept under the correct conditions at all stages from manufacture to actual use which of course can't be guaranteed. Other products generally don't have the correct species of nitrite eater required although I have read positive reports of Microbe-Lift Nite-Out II - it's not clear what its recipe is, though.

I use Tetra Safestart, always successfully, in situations when I'm setting up a hospital tank and remove a portion of filter media from the main tank filter, then top this up with new filter media embedded with Tetra Safestart. It may be that this success (i.e. keeping ammonia and nitrite at 0, and not having nitrates rise more than 20) is simply because I have the hospital tank already cycled with the portion of cycled filter media, rather than the Tetra Safestart, but having the additional filter media wrapped around it embedded with Tetra Safestart provides me with peace of mind.

It could be a Chinese algae eater [ https://www.fishkeeping.co.uk/modules/ ... sheet.php?caresheetID=126 or https://www.seriouslyfish.com/species/crossocheilus-atrilimes/ or https://www.seriouslyfish.com/species/crossocheilus-langei/ ] or an otocinclus [ https://www.seriouslyfish.com/species/otocinclus-cocama/ ] but NB it would be important to determine which as they have very different requirements for care, most importantly tank size requirements.

If it is harassing the goldfish, and particularly to the extent you describe and which could result in stressing the goldfish to the brink of injury, illness or death, then it needs to be separated from them. Your priority will be to establish which of the above it is, and, if a Chinese/Siamese algae eater or similar species which requires a much larger tank, then either upgrade its tank ASAP or else re-home it via www.aquarist-classifieds.co.uk

As it's difficult to tell from the information you've provided, and without the water quality and water parameter information, my inclination is that the fish is more likely to be a Chinese/Siamese algae eater than an otocinclus as the behaviour seems very different from the timid/gentle behaviour of an otocinclus and which would likely be intimidated by the presumably larger goldfish.

The goldfish also require a very different and much larger environment to a 57-litre tank. The reasons behind this can be read in https://www.fishkeeping.co.uk/articles ... -size-life-expectancy.htm and http://injaf.org/aquarium-fish/the-goldfish-section/ . If you can't provide them with the size of tank and other aspects of care they require - https://www.fishkeeping.co.uk/articles_12/keeping-goldfish.htm and https://www.fishkeeping.co.uk/modules/ ... esheets.php?cat=Coldwater for the appropriate Caresheet for the species you have - then, again, I'd advise re-homing via www.aquarist-classifieds.co.uk If they are single-tailed / common or comet goldfish, then you could temporarily home them in a 145-litre Really Useful Box http://www.reallyusefulproducts.co.uk ... eshop/rub/b145_0litre.php until the spring when a nearby pond owner could hopefully take them on - Aquarist Classifieds might advertise such locally.

Hope that's useful.

You're absolutely correct about higher PH increasing the toxicity of ammonia. Therefore, a product which can increase the hardness but not affect the PH would be ideal.

The actual ingredients in the Seachem products and the Microbe products seem to be a closely guarded secret. My LFS believes they are the same ingredients although my personal experience is that the Microbe products leave more of an oil slick/film on the water surface than the Seachem ones so I don't think they necessarily are the same. There might be no harm in swapping to Seachem, see if that makes a difference until the tank is definitely cycled (or the ammonia level drops and remains at 0 or even 0.25), then you can always use up the remainder of the Microbe products once passed that stage.

I'll PM you a link to another thread from elsewhere which sounds like a similar situation to yours - worth a read.