Fish stays at bottom

Question
I have a 40 gallon tank with two gold fishes and one Koi fish. Since 2 days I am seeing all three fishes are lying at the bottom of the tank most of the time. They are active and come to the surface when I feed them. Here are some points that notice.
1. Stamach (for gold fishes) seems to bloated
2. Erratic movements sometimes
I have changed the 20% of water 2 weeks ago and changed 10% of water yesterday. I have added required quantity of aquarium salt (for the 40 gallons of water). The aquarium temperature is 68 degrees. I have tested the water quality and the test results are: 1. pH (7.2 to 7.4); 2. Ammonia: 0 ppm; Nitrate: nil
Appreciate for a help.

Answer
Hi Smitha;

Based on their behavior it could be one or more of a number of things; parasites, bacterial infection, toxin poisoning. Or, they may simply be constipated. Try fasting them for 3 days. That means no food for 3 whole days. They aren't going to starve to death. They will be fine. It simply gives them a chance to clear their digestive tract and hopefully relieve their bloating. After the 3 day fast, give them cooked and peeled green peas, no other foods. Feed the peas for 3 days and if they seem to lose the bloated look, start givving them a little regular food too. The peas act as a laxative. Hopefully they will be feeling better and act more normally and the problem will be solved. If that's not it...

Look for signs of parasites or bacterial infection on their skin or fins. Do they have any spots, dots, whitish patches, etc.? Does it look like they have whitish or gold colored dust on their skin?

I didn't notice a reading from a nitrite test. (Or, the nitrate is being mistaken for it. Pretty common actually.) If the nitrite is elevated at all the fish will act like yours do. Let me know and we can go from there.

You should know that your tank is far too small for koi. Those guys get to be over 3 feet long and need 1000 gallons (yes, one-thousand gallons) for one koi and then 100 gallons (one hundred) for each additional koi. They don't grow terribly fast as they pass the juvenile stage but a 40 gallon is already too small for the first year. They start to leap and thrash around when they don't have enough space. Sometimes they even injure themselves or break tank tops and glass. (yikes!)

If you could tell me more about the fish and their tank such as;

How long has the tank been set up?
What kind of filter system?
When was it last cleaned?
How long have the fish been in the tank?
How big are each of the fish?
How much salt did you add exactly? Have you ever added any before? If so, how much and when? How often?
What kind of food do you feed them? How often? How long does it take for them to eat it all?
Do they ever rub themselves on things in the tank? Do they 'twitch' as if something itches or irritates them?

Let me know as much as you can and hopefully we can figure this all out...

At Your Service;
Chris Robbins