My Kribs Spawned Twice But...

I set up a 10gal tank with 5 Cardinals and a pair of Kribs. I set it up for
my 10 year old son who has taken an interest in fish for some time now. I
thought Kribs would be an interesting fish for him to breed, given their
parental instincts.

Went to the LFS and picked out a plump female and a male. Although far from
full grown, I would say they were more mature juveniles. On day three of
getting them home they spawned on the inside of an inverted clay pot with
the bottom cut off. For the next 2 days the female religiously guarded and
fanned the eggs. The male didn't seem to be interested at all and just
foraged for food all day. On day 3 the eggs were gone and the female was
out looking for food with the male. No sign of any fry. I understand it is
relatively common to be unsuccessful the first time they spawn.

Within 8 days they spawned again in the same pot. I did notice a
significant difference in the male this time. He took a more active roll in
guarding the area. He even spent some time in the pot along with her (she
seemed to be ok with this). From the side of the tank I could see some of
the eggs inside the clay pot. They looked good, didn't have any signs of
fungus which led me to believe they got fertilized. The morning of day 4
the eggs were gone but the fish were tending them as usual so I thought they
were bouncing off the bottom inside the pot, not yet free swimming. Later
that day both fish were out looking for food and abandoned the pot. I have
heard that they will move the newly hatched fry to new locations but there
are no signs of this. It seems to me that one of the two (or both) ate the
eggs/newly hatched fry again.

Is this something they have to work out themselves or am I not providing the
right environment?

Set-up facts that may help:

UG filter with air risers.
Standard coarse gravel about 1/8 to 3/16" dia. Is there any way the fry got
caught up in the gravel. Although it is an UG filter, it is driven by a low
rate pump, I can't believe there is any real velocity to speak of.

pH 6.8 - 7.2
no measurable ammonia or nitrites.

Is there anything I should do differently or chalk it up to their
inexperience (or perhaps mine) and let them keep trying as is.

What a shame, they seem to make such a nice couple and get along very well.

Thanks to all,
Steve