From what I've heard, most fishkeepers said their GATF killed themselves after reached 2' by smashing its face into the glass. Big ones are either live in either HUGE glass tank or small pond. Some able to keep it in community but you need feeders swimming around and every ATFs need to be in full.
I have one 16" GATF in 280g tank, here are information I could share:
1. The tank should be at least 72" x 30" x 30" for ONE.
- GATF will always swim around and in some case, darting around when it was spooked. Having huge tank decreased odds of killing itself darting into the wall.
2. For long term care, there can be ONE or NONE ATF.
- For some odd reasons, when ATF reached around 10", they became territorial and became aggressive towards everything it could eat or kinda look like them.
- If kept in shoals, be ready for bite marks/ broken fins on weaker ATFs.
- I lost a 14" to then 13" GATF. Never trust this thing. Ever.
3. Please use black sticker on 4 sides.
- This gives your fish "indications" about how much farther it could go.
- Not to mention it made your ATF felt secured.
4. It needs tank mates, but make sure you have non-aggressive ones.
- I have trouble with Bala Shark/ Insignis/ whatever they are, except Albino Tinfoil Barbs and Red Tail Barbs, they went along with GATF nicely.
- If tank mates show any signs of aggression towards GATF, you may want to remove it fast.
4. Use Wavemaker for tank circulation, if possible.
- My GATF hates Powerhead for some reason. End up loving giant Wavemaker.
- ATF came from area with strong current. A small flow will calm it. Not too strong though.
5. There should be a distance between the tank and people walking around.
- Getting too close to the tank/ knocking/ touching/ suddenly appear in front of it may be the cause of your ATF's death. 'Nuff said.
- This is also why black sticker on 4 sides helps.
- Some big GATF may not be spooked so easily but better safe than sorry.
6. If possible, pick the best one from LSF.
- It may be not possible for many, but my last GATF is the one I picked from the herd at LSF. Got him at 4". I chose a big, healthy one which ate feeders already and not just suddenly darting away from my hand. It also has the most calm personality.
Hope that helps. Today mine spooked only when I try to catch something from the tank or suddenly light a flashlight into it. Trying to prolong his time as much as possible though.