Cautionary Tale For A QT Tank

Hiya, thanks for the advice on previous thread for snails and shrimps. But have some sad news to report. My latest 3 pearl gourami have suffered a casualty.

The biggest one, who was always a bit pale (don't know why I actually picked her from the shop) was breathing really hard over the last few days, looking quite swollen and pretty much sitting at the bottom of the tank. I moved her into QT tank but she died within about 15 mins of getting moved over. At least it was quick, but hope it wasn't something I done to bring on the sudden death 

Lessons Learned : -

The morale of this story for any other newbies out there is don't get pressurised by shop staff standing poised to grab you fish, or for that matter take fish from a tank where there are poorly looking ones. Make sure you're really comfortable with the fish you are getting and if not don't get them. I knew from the moment I got the one that's died that she wasn't right, so why did I pick her 

If you got a QT tank use it!! if not get one.  I put my three new gourami's straight into the main tank, even though I have a QT I'm hoping the one that's died was just a poorly one from the start and hasn't unleashed something evil in my tank.

Sorry to read about this, @Lynne W. Fishkeeping is definitely an ongoing learning curve, irrespective of how long a fishkeeper someone has been.

I've learned a couple of lessons this weekend myself and spent last night and most of today feeling like this too as I ought to have known better:
* A fishkeeper probably needs a quarantine tank (for new fish) and a hospital tank (for sick fish) in addition to the main tank, with a spare heater and filter for each. Even although the QT is just a temporary home, it probably needs to be of adequate / the required size those fish would ultimately need (which is where I think I've made a mistake), while a HT can be much smaller and a plastic type one would probably suffice. Having a QT and a HT also allows the possibility of treating any sick fish in the HT in the event this occurs in the main or quarantine tank while both are in use.
* When dosing any medication or products in the tank, best to dilute this in tank water before adding - I poured a dose through the feeding hole yesterday and the fish dived straight for it (and now I'm wondering if a fish which kamikazed out of the tank may have done so after an acute reaction to ingesting a concentrated dose).

There are a couple of interesting articles here about quarantining:
https://www.practicalfishkeeping.co.uk/features/articles/how-to-set-up-a-quarantine-tank
https://www.fishkeeper.co.uk/about/faqs/do-i-need-to-quarantine-my-new-fish-and-if-so-how-do-i-do-it

Just to add to Littlefish's good points, another couple of pieces of advice when flushed with the excitement of potentially buying new fish:
* If you live locally enough to a LFS that you can easily return there, then:
*** it's often a good idea to go deliberately without purse/wallet on the first occasion, to avoid succumbing to temptation/impulse/sales tactics - this gives time to go away and do any additional research about suitability/compatibility, have a think, etc.;
*** if research plus your desires have a 'match', then return on a separate occasion and see if you still feel the same way about those fish and if they still look healthy or not, taking into account those in neighbouring tanks and all the other issues which might spring to mind once you've been able to think more rationally rather than flushed with excitement; if all seems good, you could either purchase on this occasion or even reserve and only purchase them on a third visit, once you've checked all again.
This is by no means foolproof, as fish may still be harbouring something which isn't noticeable, but perhaps a helpful rule-of-thumb to go by.

I take pictures of things (fish & equipment) and tell them that I'm going to do more research at home to make sure things fit in with my plans. Useful if they put the latin names of fish on the labels and there are a lot of similar looking fish with similar common names.
A fall back option is the phrase "just browsing". It works in a similar way to dealing with cold callers offering home improvements when you say "it's a rental property" (even if it isn't).
I have just read the links that fcmf posted previously, and agree with using different quarantine tanks for fish from different sources.
The links say to quarantine for 2-4 weeks. Experienced keepers on this forum have recommended a month. I try to always adhere to this, though patience is not my strong point - which often makes me wonder how I've ended up with fishkeeping and gardening as my favourite hobbies.