kaiseri larvae problem

I got this year my first kaiseri eggs and after 3-4 weeks larvae from them, but than I had the following problem:
some larvae died 1-3 days after hatching: they became more and more inactive and within 1-2 days were falling to a side and lying motionless around. Not all but majority of the later dead larvae developed a "blown up" belly, under the good visible yolk sac.

I kept the eggs according laying periods in groups of 5-10 in separate small boxes.
I used 1 day old tap water with some small calcium stones laid on the ground. water temperature 18°C
In the same water (taken immediatly from the tap without waiting) I raised Salamandra larvae successfully. Chlorine level is very low, ph around 7.
First I thought the Ikea boxes I used might be the reason because of some chemicals in the plastic.
But larvae from glas tanks died as well.
These larvae that survived the first week made it and are now 20-40mm long.
But a significant number of larvae (70%) died as described above.
Does anybody of the Neurergus breeders here in the forum have similar experience?
What could be the reason: bacteria, water chemicals...?

A few questions for background:

Have you raised other caudate larvae before?

Sniff the water - does it smell?

Any aquatic plants with the larvae?

Its not my first try to breed newts.
I raised the last years Axolotl and Salamandra salamandra as well as Triturus karelini successfuly.
The water was changed all 2 days and did not contain any plants.

From what I've heard from Michael Shromm, the eggs and larvae need fast flowing water to keep them healthy and allow them to develope properly. You might want to try contacting him through this site to see if he has any more suggestions. Good luck!

Last year the eggs and larvae I left with my adults did much better than the eggs and larvae I raised in sweater boxes. I contributed that to better water conditions and faster moving water. This year I'm hatching some eggs in a sweater box with lots of circulation from an airstone and a few live plants. I set up the container before I had eggs to let it season. I used water from the adult tank. I only do very small water changes and so far all is fine. N. kaiseri larvae seem to be sensitive to water quality issues and big water changes. I keep my axolotl larvae and fire salamander larvae very different than my Neurergus kaiseri larvae.

I also plan to set up an aquarium for kaiseri larvae. I'll set it up more like a permanent tank with live plants than a larvae rearing set up. I'll use sponge filters for filtration.
Michael

After the problems in the beginning all of the survivors do well.

From egg laying until now I do it like this:
I change the water all 2 days nearly complete (except one group*).

2 weeks after hatching I added some plants. Animals are kept in small plastic boxes (15 x 20cm)
with 10cm water level and some plants. Since they reached 25mm length they like to climb in the floating plants during the day and come down to the ground to feed in the night.

*One group of 8 specimen lives in a plastic box with many plants and one third of the water is changed only once a week. These are the biggest at the moment: 2 month old and 40-45mm long.

I found that calcium in the water does not make a difference. I tried with and without limestone in the water. As well I tried with and without and air pump as used for fishes and can not see a difference in growing except one group*.

Due to observations in nature kaiseri larvae live in slow running water (or rarely in standing water) on muddy ground and in spring pools with more or less clear water (observations of friends in Iran). They are not the stream type as crocatus or microspilotus.