You just need to be sneaky when netting fish - and have a large net or 2 (pick up a 25-30 cm fine mesh, pond nets may be too deep to manage easily)
The trick is to never “chase” with the nets, just slow movements and once fish have gone into flight/fright mode, just leave net in tank and walk away
You can also “load” net with some frozen brine shrimp (I always feed frozen foods, obviously flake will break down too much, pellets may go through netting) and just rest it near the surface, most tetras will be quick to investigate - you only want to place a (very) small amount of food in the net each time, as you want fish to remain hungry
Slowly, carefully lift net - try to avoid startling fish too much - transfer fish to holding bin
You can often scoop several fish just by having the net in place, then feed a small amount of floating food - as fish haven’t been fed for 1-2 days, they will readily come to surface, and again you can scoop some silly tetras (NO chasing)
This can usually be repeated a couple times, and you should have 2/3 to most tetras, the remaining will be much more timid re few in number, so try again another day (or in a couple hours depending on fish)
You can also return the healthy fish to the tank, but I usually wait until I’m convinced the last couple won’t come out on their own
Also a bottle trap (the quickest version, loads more 10min videos
) - I prefer this method for dwarf cichlids, Corydoras etc
- just select a bottle that has a wide enough mouth for your fish of interest (I use a rectangular shaped orange juice bottle, an occasional fish will sort out how to get back but that takes time)
- I skip the bottom holes as I don’t want water dripping as I walk across the room
- rather than string I just cut a few notches and use some large elastic bands to secure the top (this makes bottle very quick to set/remove fish)
A
quick-fit version
- no video but the discussion covers some useful tips
I don’t feed fish for 24h, then set up my bottle trap with a mix of their favourite food (a bit of frozen brine shrimp due to its irresistible aroma, blood worms as small fish take time to swallow these)
Once bottle has 10-12 fish, I remove bottle and pour fish into my holding bin
Reset bottle and capture more (I once left the bottle overnight and it was too crowded in the morning - fish were obviously stressed (and some shrimp had crawled in as well))
Of course as tetra numbers decline, the last ones will be more timid, so wait several hours or overnight before trying again
While you can treat all fish in the 1200
- plants may react poorly to the medications (especially as you may need to treat for an extended time or repeat treatments)
- shrimp, snails may die (often not on day 1, but over treatment time)
- dead fish may be lost in the plant growth and other fish will cannibalize (a very bad idea in this situation)
ETA when netting fish, dropping the water level may be helpful
Place your nets and wait for tetras to swim into the area, and so on
Depending upon your fish, this can work very well OR fish may decide to hide in plants if filter etc it off (in response to a large change in normal conditions)