Do you see any problem with these fry?

I have been very puzzled for a long time about the look of my ABN fry. I have fries in 3 separate tanks, 2 matured and 1 new. Those in the matured tank look normal as in pict 1 (head to tail are evenly tapered), but those in the new tank look like pict 2, with big head and extremely skinny tail (looked malnourished). They all eat the same amount of food, same amount of WC. I am using Seachem Ammonia Alert in all tanks, indication is normal. I do at least 20-30% WC daily in all tanks.

I then moved some of the fries from new tank to the matured tank and in less than 2 weeks, they were back to normal. I am just wondering what is wrong with the new tank. Fries reared in the 2 matured tank right from the start appeared normal and those that have been moved there from the new tank, became normal in no time. However, mortality rate in the new tank is considered low though, approx 10%. Growth rate is normal in matured tank, but extremely slow in new tank.

New tank (80L): new DW (soaked in boiling water), new coconut husk, hang-on filter, air-stone
Matured tank 1 (50L): 2 bio sponge, new coconut husk
Matured tank 2 (25L): matured DW, matured coconut husk, hang-on filter, air-stone

yeah, there is definatly something going on there and i see it all the time. It looks like bloat and may well be. other things it may be caused by is ammonia ( i know you have the alert things but i must admit i dont trust them too much) or other issue in the water. I have this issue every now and again and i find its associated with cleaning my filters in my grow out tank so i suspect it has something to do with ammonia spikes. but im not sure.

Id say a water condition issue! how big is your grow out tank?? and what is the PH and Nitrite's??

Thanks for the fast respond. So, there really is some problem with these fry. I have 2 other tanks to compare, that is why I thought those in the new tank (and only in this tank) look kind of funny all these while, but can't pin the problem because not many casualty. I do not have nitrite test kit on hand, so not checked, but have got PH reading for each tank though.

1) New tank, 80L (2x1.8x1.8') - PH 6.5


2) Matured tank, 25L (1x1x1.6') - PH 5


3) Matured tank, 50L (2x1.2x1.2') - PH 5
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Your PH is way to low... ......it wants to be around 7.....the reason why its so low is because you just have bogwood/driftwood in there with nothing else even no substrate....bogwood will naturally lower your PH......
There are a few reads on here that explain about raising and lowering your tanks PH have a look around or i will find it for you shortly......

Curby FTW!!

Thanks Curby, I found the thread. I happen to have a bag of crushed corals to raise the PH, will try it out, though it didn't help much in my discus tank before.

Good news guys. I see improvement in the fry now. Since Doug and Curby mentioned about ammonia and nitrite, therefore I decided to add 1 matured bio sponge from my discus tank and also added lots of PSB Bacteria daily. Within just a couple of days, I see the fry pooing and the belly is not so bloated already, the tail seemed to be gaining slight weight. Will continue to monitor.

As water was crystal clear, it has never crossed my mind that it could be ammonia/nitrite problem, thanks guys.