Please help. I have a 40 gal tank with 4 veiltails....1 is sick. For 4 days now he has been sitting at the bottom hardly moving for hours and hours. Tank is established now (1 month old)....ph at 7.8....nitrates 0, nitrites 0, alka at ideal...and no ammonia. water temp 70...boys eat a varied diet...although I must confess I had not been soaking their flakes when on flakes. Highend filtration system....other 3 fish are fine....and they are not picking on him. He still has an appetite...and will swim up with no problems when I feed (once a day)...but as soon as he is done he goes back down to the bottom and sits unmoving again. I did a partial change of water yesterday...and checked the quality again....and I fed him frozen peas (shelled & mushed) last night....I half expected him to be dead this morning....but he surprised me and is still on the bottom motionless. He does not look swollen as far as I can tell...is it possible he ate a rock?
Of other note...I cannot see any Ich....nor lesions of any kind....I do dechlorinate the water and all 3 other fish are happy and healthy. Please HELP!!!!!!

Hi and welcome to the forum

A bottom sitting fish could be a swimbladder issue, but he can swim to the top to feed.
Are you sure its a male as a gravid female could have the same problem, how big without tail is the fish?
Bacterial isues also spring to mind.
How much water have you changed and how often and how much do you do water changes?
With you saying its established, have you seen it go through a cycle?
Any chance of a pic?

Sick Veiltail.....The aquarium has gone thru a full cycle....I change water weekly at 40- 50%....and vac grav at same time......also of note....he is no longer interested in food ....just tried some mashed peas again and couldn't get him to come to top....he is dragging his fins......and I have no idea if HE is really a gravid female!!!!! Size is about 2 - 3 inches excluding tail.......

Ok first thing I am concerned with is the 0 nitrates. This means the tank isn't cycled. Whether or not it went thru one and then for some reason is crashed?????
So with no nitrates you don't have the biocycle in place to take care of ammonia when it appears. Although it is good there isn't any, but with 0 nitrates that water quality is bouncing around.

When you say it fully cycled, did you have nitrates at one point? And if so do you know why they are 0 now?

sorry...should of been more precise.....my nitrates are not 0...but in acceptable mode at 20.....I guess my biggest question right now is should I remove & quarantine him?

If you have a tank at least 10 gallons then yes you should. It sounds like it could be a bacterial infection of the swibladder which is grounding him.
Its unlikely that its a gravid female due to the size of the fish.
Can you get medicated food at all?

That is better.

Sandy is most likely on spot since the water is ok.

Ok....I can do the hospital aquarium...but I'm a little confused as to whats the best procedure. Someone said to have the level of water at only 6 inches.....do I go with this method and warmer water and give meds....and do I need to put water in from the other aquarium in it? please advise....

You can have the water lowered to 6 inches as this will take the strain off the fish.
Use half tank water and half fresh and any filter should be gentle and already cycled if possible.

How is the fish doing today?