Pla Duk floating head up after eating...but healthy?

[ThaiFelix]

Hi everyone. I am a newby with PlaDuk and need some help. Concrete tank 3 mt x 2 1/2 mt, water level 40 cm. About 350 fingerlings (about 125mm.) Although we had some initial problems losing about 10 fish a day thru some bacterial disease, after a salt treatment suggested by Udon Fisheries office we have not lost any. Fish look healthy, eat like they havnt been fed for weeks but after feeding there is always a dozen or so that float lethargically with the heads up and whiskers just on the surface?? First we thought it was bloating from the small commercial floating pellets and it was suggested that I soak the food first (about 10 mins). Still having the same results. Saw something on here yesterday about "head float" but it didnt give any details and today I cant find that same post. By the way I do a 50% water change twice a week. The water comes from the next moobarn and I am told it is untreated and comes from a 90 meter bore. This water appears very clean but does have a lot of minerals judging from the salts that build up on the bathroom fittings, tiles etc. Anybody have any ideas??

Thanks in anticipation.

[ThaiFelix]

Failed to mention that all fish are back to normal after 10 to 15 minutes after feeding. I am using InteqC 4641? small pellets, and feeding twice a day.

[colinneil]

Did you have this problem just after you changed the water?

[ThaiFelix]

Did you have this problem just after you changed the water?

No, only seems to be after eating.