Are my zebra loaches happy?

Hi all,

I have three zebra loaches.. most of the time they hide.. somewhere in the
plants, but when they hide, I cannot find them.. but every few days, I
manage to count three so I know they are alive.

the question is, when I feed the tank, I'm always wondering if they are
getting enough food. I used to be a pretty spare feeder, but these days,
I'm trying to get some food to reach the bottom of the tank so that the
loaches can find them and eat them. (food= flakes, frozen bloodworms, loach
pellets, etc) Most of the food that is drifting in the tank gets
immediately snatched up by other fast swimmers (and hogs. they're getting
fat since they're eating the loach's share, which is not great either)

but I rarely see the loaches eat..

should I worry if they are eating enough? or are they an efficient scavenger
enough that I won't have to worry? I've had them for about 2 months now, I
think.

also.. I'm not sure if they are all that happy in the tank. most of the
time they are hiding (day or night).. and I see them listlessly lying on the
gravel (sometimes sideways, sometimes normally.. but apparently loaches
sleep in bizzare angles, so..). one of them almost looked like a
white-black zebra and not the yellow-black zebra. but when three of them
congregate, they seem to frolic with zest... I don't think they are ill
physically... but my gut instinct says something isn't quite right.

I know they are shy species in general. so I'm wondering if there is
something else I can do to make them happier.. (if i'm convinced they just
need more pals, I'll try to find more zebras.. but they're kind of hard to
come by)

I have two driftwoods that are in a shape of an "L".. they are placed so
that it makes an arch, 2inches vertical opening, probably 5-6in long width.
I also have lots of sword plants.. do they need more hiding places (perhaps
bury a sideways espresso cup into the gravel?)? or if they can hide in the
plants without me ever seeing them for a few days, do they have enough
hiding place to keep them happy?

tank: 37G
temp: ~76F
gH/kH: ~3 (yes.. very soft..)
pH: ~7.6 (tends to drift between 7.0 and 7.6 due to the plant respiration
during the day)
heavily planted (zero ammonia, nitrite, nitrate)
lots of current and surface ripple (HOT magnum and two powerheads on UGF,
all outputs directed towards the surface intentionally). none of the fish
including otos hover near surface even when pitch black dark, so I assume
the water is well oxygenated
companion fish in the tank (they don't bother the loaches at all) SAE's,
gouramis, WCM, danios, otos
tank is somewhat ridden with algae (the type that films the glass and
blackens the plant leaves) but not bad since SAE's and otos seem to keep
them under control

Otos are getting fat and seem happy, so the conditions can't be all that
harsh (I think they are the most delicate of all the fish I have in the tank
in terms of water condition). any suggestions that will help them more?

linda