xqizit wrote:
Hi,

Itook 50% water and gravel from my main tank to start up the fry tank
so there should be no problem with it not being cycled.

Moving water and gravel does not create a sufficient bacterial colony to
prevent cycling. These days, unless you're still using undergravel
filters, the amount of bacteria in the gravel is minimal and there's
actually more of a chance of hitting an anaerobic pocket than transferring
good bacteria. Plus I prefer my small fry tanks to be bare-bottomed so
that waste can be more easily spotted and syphoned away. But back to the
point at hand, the only way to prevent cycling in a fry tank is to use
established FILTER media. For this purpose, I keep a hydro-sponge in the
main tank to transfer over to fry tanks as needed.

The ammonia as checked was fine. I have been doing water swapping from
the main tank every few days. My main tank is fine and my fish are all
breeding happily. (hence the reason for the fry tank)

What about the nitrites? I find this to be an even bigger killer than
ammonia in fry. To understand this, you need to understand what nitrite
poisoning does. When nitrite is absorbed into the blood stream, it
converts hemoglobin into a form that no longer transports oxygen. Fry have
a smaller volume of blood than adults, so they can more quickly reach that
critical point where they no longer have enough active hemoglobin. They
will essentially suffocate from the inside. This will manifest as being
sluggish or with respiratory distress, so your theory of tiring from the
filter flow might have more to do with nitrite poisoning than just simply
tiring out.

And while speaking of filters, I'd like to second Amatuer Cichlid's
suggestion of losing the HOB filter and using a sponge filter instead. I
particularly prefer the wider hydrosponges (4" diameter and higher). They
seem to be really good at providing surface area for bacterial colonies
and fry like to graze on them as well, so they don't create too much
suction. When they get larger, you can switch them to a grow-out tank with
HOB filters or larger sponge filters. If you feel you must stick to a HOB
filter, get a package of AquaClear mini sponges, cut a slit in one and
stick it over the intake pipe. This will prevent the fry from getting
sucked in.