Too small of a quarantine tank?

[MultipleTankSyndrome]

I was going to pick some cardinal tetras up for Boxing Day sales, but the quarantine tank I was planning to put them in may be preoccupied if possible health issues with my existing fish don't go away: https://www.monsterfishkeepers.com/...al-cure-on-wasting-disease-and-flukes.745082/

However, should this be the case, I do have another, smaller tank. It is about 40x13x20 cm (LxWxH) and comes out to 10 liters in volume.
The dimensions of the tank align with the minimum 6x the length and 1.5x the width rules of thumb that Practical Fishkeeping and Seriously Fish give (considering cardinals only top out at 3-5 cm), yet AqAdvisor says the following about a school of 8 being in there.


Now, while this setup will obviously be temporary (standard quarantine of 1 month or so, unless health problems show up at the end of that month), would it really be so overstocked within that timeframe? I do have my doubts considering how it lines up with the previously mentioned rules of thumb.

 

[..puSkar..]

RD. duanes

 

[jjohnwm]

Sometimes, no matter how good the deal may be, you just have to say "no" to buying new fish...and not having a place to keep them is one of those times. Your tank is 5 inches wide. Regardless of what the clowns at Practical Fishkeeping or AqAdvisor have to say about the numbers...no fish belongs in a tank 5 inches wide.

The one-size-fits-all "formula" that is used on those sites might have some merit when applied to medium-sized fish in medium-sized tanks, but they really start to fall apart when used on very small or very large specimens and tanks, or unusually-shaped fish, or very active or inactive fish, or very high or low bioload fish, or...just about anything, really.

Don't believe that? Why are they so completely opposed in this case? Because they are both so simplistic and unrealistic that neither can be trusted.

And, by the way, how do you filter a tank like that? With a HOB that will plaster the fish against the sides with its current...or with a sponge filter that takes up half the tank space?

So, IMHO, just say no. To repeat: no fish belongs in a tank 5 inches wide. No amount of calculating changes that. YMMV.

 

[MultipleTankSyndrome]

Thank you jjohnwm for pointing out those many variables. I guess the desire to take advantage of those Boxing Day sales got the better of me haha.

Unless RD/duanes/anyone else has anything else to point out, I'll be looking into a Rubbermaid stock tank of at least 40-50 liters instead. If I don't get one between now and Boxing Day, no cardinals.

Edit: would be filtered with live plants. I have a lot of hornwort on standby.
I suppose that at least with the Rubbermaid, the filtration is more practical.