Wrigglers dying off.. with broken yolk sac!?

[GarageAquarium]

Hey guys, I just had my first apisto eggs hatched - got around 50 eggs and 90% had turned into wrigglers. I’ve used a few drops of methylene blue to fight fungus because both of first 2 batches that I left to the female apisto to take care of had some fungus problems and eventually got eaten up by the female so I went pretty conservatively and added a few drops of MB just in case.

So I heard that we need to do a few water changes to get rid of the MB and I did a 20% water change using the water from the breeding tank ( same water I used to start up the hatching box). And 12 hours later I noticed that yolk sac of around 10 wrigglers turned white and they stop wriggling, some yolk sac even oozing out like a fried egg ( the bottom one in the picture)…
I also notice that the dither platy and the female apisto in the breeding tank did a few flashing (no white spots on them at all) on the driftwood yesterday but breathing still seems fine. Would it be possible that these dead wrigglers were attacked by microscopic worms like gill flukes or something ?
I think I will stop doing any water change until they are free-swimming, if that could potentially change the osmotic pressure to break the yolk sac or something..

 

[yukondog]

In the few years I have been breeding apisto's, I have never seen this, but at this point I would not stop water changes.
What are you parameters? Size tank?

 

[LowConductivity]

What size container are they in. Is it established? Is it cycled?

 

[Fishytime25]

How much MB did you add? Maybe it was a deadly high amount.

 

[GarageAquarium]

In the few years I have been breeding apisto's, I have never seen this, but at this point I would not stop water changes.
What are you parameters? Size tank?

I am new to breeding apisto but this is so bizarre to me!
It’s an aged 20L small tank (previously for raising gourami fries), and I’ve been using RO water (ph is 6.8 & TDS<100 out of tap) and I am doing weekly 25% W/C so the nitrate shouldn’t be <15ppm.

What size container are they in. Is it established? Is it cycled?

It’s a 20L tank with a fully cycled homemade sponge filter ( strengthened up with additional media beside sponge), it was a fry raising tank so it’s quite established.

How much MB did you add? Maybe it was a deadly high amount.

I think you may be right, I couldn’t stand seeing fry dying one by one like that so I took the risk of shocking them to death I’ve transferred them into another hatching box with just RO water( temperature acclimated), and touch wood - no casualties since then!

Here’s how I added MB: I started with a smaller hatching box so I added two drops. I had airstone oxygenating it all the time and the next day I found that the water lost the blue colour ( MB reacted with oxygen ?) Then I transferred the terracotta pot with eggs on to another box with 2times volume and added 8 drops(less than 0.5ml), and I got a very light blue water which looks safe to me tho.

But I got nothing else to blame except for the MB concentration, because I’ve even observed the water sample with a cheap microscope to try to spot any worms and all I could see was some harmless white dots swimming around the carcass showing no interest to the fry body..

 

[yukondog]

Is this a 20 long or liter?
What type apisto?
What size is the breeding tank?

 

[GarageAquarium]

Is this a 20 long or liter?
What type apisto?
What size is the breeding tank?

It’s a 35wide x25deep x25high (cm) tank and this is the tank they(hongsloi) bred, but I actually pulled the eggs so eggs were hatched in a hatching box (25x15x10cm).

 

[yukondog]

The tank is really to small, and why did you pull the eggs/fry?

 

[GarageAquarium]

The tank is really to small, and why did you pull the eggs/fry?

Yes it is a bit too small volume &floor size wise for them so I had to add a lot of sight breaks to allow the female to hide, I do plan to upsize the tank but I need to rearrangement my place to fit in a bigger tank.
I heard that it only takes apisto another 2-3 weeks to spawn again and I knew I was going to make more or less mistakes. To maximise the yield I was planning to get them to spawn 2 batches, I would raise the first batch myself and the female would raise the 2nd after I clean all snails in the tank. So now she’s being conditioned for the next batch. ( hopefully I still have fries left when she spawns again)