I'm sure everyone experiences this but

[ron1njdds]

You're looking at your fish and can't find one..after a thorough search you finally give up. Assuming it died, what do you do? Nothing..just let it decompose and hope your biofilter can keep up (we are talking about a small dither fish in a 20L tannin biotope tank with 85 gallons of filtration power) or tear everything apart and try to find it? In a heavily hardscaped and planted tank this seems crazy to me. What do all of my experienced fellow fish keepers do?

 

[Mbkemp]

I keep looking and they generally pop up at some point

 

[MickeM]

(If it was a female from an Apisto-pair missing in a tank I`d wait for at least a week to see if she turns up from a cave with free swimming fry. )

If it`s the last specimen of fish with no medical history gone missing , I would do a smaller waterchange (5-10%) , and then siphoning off/cleaning a small amount of the bottom-sand/gravel if possible. I might do this 2 or 3 times before adding any new fish!!
If you are a not an experienced tank-owner , the best could be to ask an experienced one to have a look at the tank/set-up.
If you`ve lost more than this last fish in a short period of time I`d change the strategy and maybe lift all the interior out with the water (to a bucket/quarantine tank) and then clean+ restart the tank..
This is a common way to do it.. Especially when you keep+breed many species in several tanks at once.. (Apistos, Bettas, Killies, others..)
Fish of this kind rarely lives longer than 3-5 years so death will happen nomatter if you want it or not..

If other fish are still present in your tank I`d check them up carefully for parasites or bacterial infections before adding any new fish.