Has anyone experience of Hatchet fish in high flow. I suspect it's a no no.
Yes. If you’re attempting to make them comfortable you can create a dead spot in surface flow. If it’s a spray bar you’re using blank off a couple of the holes with electrical tape. Hatchets are God’s in drag efficiency, they don’t need much of a dip in current to be comfortable.
If it’s lily pipes and it’s two sets, have them diametrically opposed. If it’s one lily pipe, put a power head/eheim skimmer/small pump at the opposite corner. Creates calm mid tank at surface level.
This all is based on presuming a lot about your setup but principles still apply.
Watched hatches sit in the full blast of a 3000 lph pump for the hell of it. Barely flicking a fin to maintain position, quite remarkable little creatures. But some respite from high flow is a good goal for the setup if you want them happy.
You can also use taller plants or hardscape to deflect some of the flow and create sheltered areas.
@mort ’s suggestion is excellent. Any plants growing out the of water also provide shade from your lighting, fish don’t have eye lids and surface dwellers get the brunt of it. Also good rolling dry food down leaves (swords) as they seem to get a buzz from being fed in a more natural way.