Half Hatches

Do many people get half hatches consistently? I would say that most of the time my hatches come on 2 different days.  About half the first day and the other half the second day.  And there seems to be different survival rates.  Sometimes the first hatch is hardier and sometimes it is the second hatch that has more success.  I guess this is prematurity vs yolk sack depletion.  
 
When you get half hatches, do you use 2 different hatchery tanks?  Or do you add the next days larva to the hatchery tank from the night before?  I have always used 2 tanks, thinking that the first tank water would be slightly fouled already and a shock in parameters.  

I have split hatches often. I don't know why it happens, and it doesn't seem to always happen with specific pairs it just happens sometimes. I usually use the same rearing tank for both nights, mostly I just don't have room for multiple setups of the same batch. Or I just let the second nights worth go uncollected.

I have split hatches sometimes too.  I had a Snowflake pair that was notorious for it, and my Darwins are bad for it as well.  I find the unhatched ones often get fungus if I leave them in the larvae tank from me adding rotifers and RGreen.  Interestingly, when I've moved unhatched eggs back into the broodstock tank for them to look after the eggs until the evening those stinkin eggs usually hatch during the day!  I come back to retrieve them and they are gone!  The parents aren't eating them (I video monitored them).
 
I think the split hatch has something to do with light and temperature changes when moving from the broodstock tank, to the sterilizing tank, to the larvae tank.  If I am VERY careful to keep lighting similar (keep eggs out of direct light from overhead lights), and match temperature really closely I can diminish the split hatch.  My split hatches usually leave a clump of eggs on the tiles, not like every second egg hatches, it's like a section hatches and a section doesn't.  Which leads me to believe it's something I am doing. However, I've also seen split hatches in reef tanks where the eggs are completely untouched - so that kinda spoofs my idea.

Don't let fear and common sense stop you! =]

i agree with EasterEggs, im pretty sure its because of the temperature.
when the temperature is not stable, the difference of development will be larger and causing some eggs are ready to hatch, some are not.

Maybe I put my foot in my mouth because my Onyx Perculas just had a split hatch and I didn't touch the eggs. Go figure...

Don't let fear and common sense stop you! =]

I never touch the eggs.  I just snag the larva.  And my temps should be consistent.  Some eggs are laid in shady areas or behind a nem, and other have light shining directly on them the whole time.  I still seem to get lots of partial hatches.  Not sure.  Maybe a question of pre natal nutrition.  Are there tricks to induce or delay hatches?

For lighting, I meant changes in lighting, such as going from light to no light, or vice versa.  Changes in conditions near hatch time, in my experience, is not a good thing.

Don't let fear and common sense stop you! =]

I have split hatches on many of my fish, and I have yet to figure out why. It also happens when I leave the eggs in the broodstock tank, and I don't think I have any fluctuations in my setups...room is heated, and it's a basement so light is tied to a timer.

Good to know.  In my experience , I would say that the longer the eggs take to hatch the hardier the larva.  Unless its a crazy amount of the time and the yoke sacks become depleted or fungus gets em.  I think I am going to see if I can keep a small amount of light on them the night of a typical premature partial hatch, and force them to hold on for another day.  
 
Also, has anyone used something like Pimafix in the parent tank to control egg fungus?  It is all natural and supposed to be safe for everything.  I had a Picasso hatch a few months ago while using Pimafix the whole time in the parent system and I had one of my best success rates.