Ram fry developing swim bladder issues

I have a batch of ram fry about 7 weeks old. They are growing very slowly, and my next batch (2 weeks old) will likely overtake them in size soon. I think the issue is that once the fry reach a certain size they are developing swim bladder issues and fading away. I haven't been able to get any past about a cm long.
I have gone through many possibilities, including increasing feeding (BBS, Golden pearls and crushed pellets) increasing water changes and introducing some treated tap water (was using RODI only).
I'm starting to think that the genetics of this batch are just not great. The male was a gold balloon ram and the female was a lacklustre GBR.
Does anyone else have any theories? If it's something I've done wrong, I'd like to sort it out before I transfer the next (very high quality) batch of fry to this grow out tank.
I'd really appreciate any thoughts.
More info:
Tank parameters are pH - low 6
Ammonia, nitrite zero
Nitrate 10-20
TDS approx 35
65 litre tank with approx 100 fry (was a huge spawn, so I've lost about 300 slowly over time)

 

I don't know about rams but with fry in general I find there's a balance between temp ( higher end of the fish species tolerance for faster digestion and metabolism) lower end temp for slower digestion and metabolism.
And the feedings. As far as feedings go, more smaller meals are better than a couple big ones so there's always something in the tank to burn, but they aren't stuffed from feedings.

I found with 2-3 large meals a day I was having swim bladder issues which lead to fish slowing down, not eating and declining/ dying.
You can technically feed small amounts every 2 hours, or go to 4-6 smaller feeding per day for faster growth without the fishes stomachs getting full and pressuring the swim bladder causing difficulties and decline.

Fry also like low nitrates, keeping it under 10 and lower will help to avoid development issues in early stage growth.

I don't know anything ram species specific, just those two things when I figured them out and found the sweet spots my fry issues cleared up and my deaths went to zero from 3-5 a day.

 

Get your TDS to 100 for breeding and raising .
Around where you are now 4-8 weeks start adding more tap .

 

Get your TDS to 100 for breeding and raising .
Around where you are now 4-8 weeks start adding more tap .

Thanks Coralbandit. My tap water is only 70 or so. Would you recommend a remineralising supplement?
Thank you -this is very helpful!

I don't know about rams but with fry in general I find there's a balance between temp ( higher end of the fish species tolerance for faster digestion and metabolism) lower end temp for slower digestion and metabolism.
And the feedings. As far as feedings go, more smaller meals are better than a couple big ones so there's always something in the tank to burn, but they aren't stuffed from feedings.

I found with 2-3 large meals a day I was having swim bladder issues which lead to fish slowing down, not eating and declining/ dying.
You can technically feed small amounts every 2 hours, or go to 4-6 smaller feeding per day for faster growth without the fishes stomachs getting full and pressuring the swim bladder causing difficulties and decline.

Fry also like low nitrates, keeping it under 10 and lower will help to avoid development issues in early stage growth.

I don't know anything ram species specific, just those two things when I figured them out and found the sweet spots my fry issues cleared up and my deaths went to zero from 3-5 a da

 

Thanks Coralbandit. My tap water is only 70 or so. Would you recommend a remineralising supplement?
Thank you -this is very helpful!

I would look for something like this if you can
Seachem - Fresh Trace
Chek the ingredients if you are a real do it yourselfer and understand this stuff.
I used baking soda, driveway ice melt and epsom salt when re mineralizing from zero .