first night death (again)

This topic has been frequently beaten here and elsewhere, but has been very infrequently beaten to death. Was that a pun? It seems that several people have had this problem, but after they seek and receive help the thread seems to die and I am left in suspense as to whether they were successful or not.
 
I have been having problems with first night death among my clown larvae for quite some time now. I have read through all that I can find to pinpoint the cause but have been unsuccessful to date. I thought I'd post about my process to see if it tweaks any ideas among those more experienced here. I have had moderate success with a few of my pairs. I have managed to get about 50 larvae to meta (and well beyond) from about 4 different hatches. But beyond that, I would guess that I've had at least 15 hatches from which I am typically left with 2-4 larvae at the 3-day point that then develop through meta. This is way too much work for a handful of fish . So, about my situation...
 
The Parents:
I have three pairs that are laying consistently right now: 1 Tomato, 1 Ocellaris, and 1 Snowflake/Blacker Ice. My issues are not related to any one pair. Although, 2 of the 'successful' hatches that I have had with the Snowflake/Blacker Ice pair hatched nicely on day 9. Since these two hatches, I have had very inconsistent hatches with this pair. A few usually hatch on day 9, the majority hatch on day 10 and 11, and lots of unhatched/fungus-covered eggs remain on days 12+ (side-note: when this started happening about 5 months ago I started removing shrimp shells from my home-made food mix). The Tomato and Ocellaris eggs hatch just fine, usually on day 8 (or 9). These pairs are maintained in 10 or 16 gal tanks with central filtration. Water is 26 to 27C and between 1.021 and 1.024. They are fed 2-3x daily with NLS pellets, Hikari Mysis, or home-made mix (shrimp/fish/squid).
 
Larval System:
The eggs are hatched in black round tubs with a central drain, 50W heater, and airstone. The tubs have a central drain that leads to a sump (I usually don't drip water until a few days have passed). Initially, the only lighting was from the room light, but this was quite dim (especially since the tubs are shaded by the broodstock tanks above). I have since added led light strips that are dimmed quite low. The room light and the lights above the tubs are on from 8am to 10pm. My most recent procedure is to fill the tub with about 10 gal of new saltwater (mixed >24 h ago) matching the broodstock salinity, turn the heater and air on, and add 20 mL of bleach. I neutralize the bleach with sodium thiosulfate about 1 h before moving the tile with the attached eggs to the tub just before lights-out. I stand the tile against the standpipe with the airstone underneath aerating the eggs. Water temperature is always within 1C of the broodstock system. I have tried using 100% and 50% broodstock water with similar results.
 
After hatching:
In the morning, lots of larvae are visibly swimming around, most towards the side of the tub. Some are already dead on the bottom, about 10% I would guess. I start feeding rotifers immediately, usually twice per day - once in the morning about 9 am and again around 4 pm. The rotifers are grown using Nanno that I culture. I feed the rotifers 1-2 h before offering them to the larvae. I also add cultured Nanno to the tub when I add rotifers, but only enough to sort of cloud the water. The water is definitely not a deep green color. The next morning, the majority of the larvae are dead or nearly dead, lying on the bottom and occasionally twitching. The End.
 
I am at a loss as to why this is happening. I don't think it is related to broodstock nutrition (tried to improve this already), water type (tried new and broodstock water), water quality (happens too fast), or larval nutrition (happens a bit too fast for this to be the culprit, I think?). My next plan is to try 24 h lighting for the first 3-4 days to see if that keeps the larvae active and feeding. The only thing I am doing to the tubs is adding phytoplankton and rinsed rotifers. Could there be something in (or missing from) either of these that is responsible? I will admit that I only eyeball my rotifer density by pulling a sample using a syringe and aim to have ABOUT 5 rots/mL.
 

Great details!  One thing that stands out is your rotifer culture.  Since you are only using Nannochloropsis, you are not fully enriching the rotifers.  Nanno lacks DHA which is vital to marine larval fish development.  There are certain compounds that are essential to life, which means that they can not be synthesized in the body, but must be acquired in their diet.   Certain amino acids, HUFAs, lipids and all carotenoids must come from the diet.  If the larvae are lacking certain essential compounds, then you will see heavy mortalities and/or deformed juveniles.  There are products in the market place that are great all-in-one feeds.  I'm sure people on here will tell you which ones to use.  I have used RGcomplete from Reed Mariculture with great success.  If you want to culture the algae, I would suggest adding Isochrysis to the rotifer diet.    The lack of enrichment for the rotifers may not be the cause of your early mortalities, but it could be a contributing factor. 
 

Im guessing that this topic isn't beaten to death because there is no real clear answer. The variables that I question are your light and your air flow. It sounds pretty counter intuitive to use a brighter light and then tint the water to shade out light but what I think this helps to do is create contrast between objects making it easier for the larvae to see the rotifers. You don't want it so bright that the larvae are on the edge of the tank, if this happens you can add more algae for tinting darker green or raise the light a little. I tint the water pretty green, way more than just a little cloudy. If the air is too high it'll stress the larvae to the point of death in one day. I turn the air way down after hatching and bump it up over the course of a couple weeks. To your point about keeping the lights on for 24 hours, I do it for the first two or three nights. It seems to help for me. 

Couple things:
1. do you test for chlorine after using the sodium thiosulfate? Pool test strips are sufficient and inexpensive.  You have to know if the chlorine is reduced to be non-oxidative. Chlorine is a killer. Also helps to prepare the larval tub a day ahead, but I've had success with tanks prepped an hour ahead. 
2. don't dim your LED strips. Lay one across the rim of your BRT so there is a gradient of light across the tank. The larvae will find the light they like the best.
3. Air should be more than a trickle, less than a boil. Put the airstone either in the center or on the side of the tank.  I prefer the side as it gives the larvae more choices for where they want to be, but other folks think differently.
4. start out with rotifers at 10 rots/ml. Five is not enough. Low light and low food density is enough to explain the losses you are having.  Figure out how to count them. There are many methods. Count them every day, and replenish them if they seem to decline.  Grow them with RGcomplete, and you won't have to enrich them.  Save the live phyto for green water in the larval tub, and get some ISochrysis going so you can have easy copepods as well.
5. Keep the water light green (or brown if that is the color of your phyto). This keeps the rotifers fed and maximally nutritious.
6. Add the rotifers to the larval tank immediatly after hatch, and keep the light on 24/7.  Apparently, fish don't need to sleep. Just hunt and eat.
 

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Thank you for all the helpful input!
 
For the next hatches I am going to work with what I have on hand - there are hatches expected this week from each of these pairs to experiment with. I will try boosting the light intensity, greening the water a little more, adding more rotifers, and 24 h light. I was avoiding too much green water as by day 3 or 4 without a large number of larvae the rotifers make a real mess of the water. I think balancing that a bit better will help and I can always start the drip of water from the sump a little earlier. I will also adjust the airflow down as that may be a problem too. I started to get really cautious with low airflow when I had a hatch that was delayed by several days completely covered in fungus.
 
I understand that Nanno alone may not be ideal. I have noticed flared gill covers in some of the Ocellaris that I have raised (none in the Tomatoes though!) and apparently that can be due to diet and water quality. I have been wanting to culture Isochrysis but haven't had any luck finding a supply in Canada, or any in the US that would ship internationally. I will work on getting this going as I also wanted to get a Parvocalanus culture going to feed some damsel larvae that won't take my rotifers. I will likely also try a prepared phyto, like RG complete, to rule out any problems with the stuff that I am growing.
 
I don't test for chlorine and maybe I should. I have just been using the same proportions of bleach and sodium thiosulfate that I use for my phyto cultures, which seems to have been working. But maybe there is some residual and the fish are more sensitive? I don't think this is the real problem because I was having low survival before I started treating with bleach.
 
 

oops, meant to post in another thread...