My fish can’t open it’s mouth, and Is resting on the bottom of the tank, has a swim then goes back to the bottom of the tank. Pet's info: Fish | Unknown - Fish

Check the water chemistry and quality first. Elevated ammonia or nitrite levels can be toxic. Partial water changes can be done to stabilize and improve water chemistry. Use only aged or conditioned water that is temperature matched to prevent further stress or shock. For goldfish, a range of 65F to 72F is recommended. Check the filter and rinse the sponge with tank water, not tap water, to spare beneficial bacterial populations and to maintain water quality. The tank may not be large enough to support 5 goldfish. Generally, 20 gallons should be allowed for the first goldfish then a 10 additional gallons should be provided for each additional goldfish. This is due to the larger than average bio load (wastes) they produce. Consider a larger tank or decrease the number of fish in one tank. Use a filter that is rated for at least twice the volume of the tank and add an airstone and pump for increased oxygenation. Plain aquarium salt (NOT table salt). Can be used as a general tonic. It will reduce stress, improve gill function, aid in any recovery and may treat or prevent minor infection. Dissolve 1 teaspoon of salt per gallon of water in a cup of tank water and gently pour it into the tank. Treat for 10-14 days. When performing water changes, add salt only to the amount of water being replaced, not the entire tank volume.

Ideally, one goldfish should have 20 gallons of water. The reason being that goldfish produce a larger than average bio-load (wastes) than other fish. One fish can quickly overwhelm a small tank and filter. If you have a smaller tank, use a home test kit to monitor ammonia, nitrites and nitrates. When ammonia or nitrites begin to rise, it is time to perform a partial water change.

Check the water quality again use a liquid home test kit or submit a water sample for testing. The local Petco may do this for free or for a small fee Aim for an absence (0 ppm) of ammonia AND nitrites. Nitrates can be 20 ppm or less. Perform another partial water change, no more than 30% total volume, at a time. Use only conditioned water that is temperature matched to prevent stress or shock. Goldfish are cold water fish and do best between 65 F and 72 F. Additionally, a 10 gallon tank may be insufficient for 2 goldfish and a Black Moor. Goldfish produce a larger than average bio-load (waste) which can quickly overwhelm a small tank and after. Ideally, provide 20 gallons for one goldfish and an extra 10 gallons per fish. The filter should be rated for at least twice the volume of the tank. Even with a string filter, partial water changes and regular cleaning/vacuuming will be needed to maintain water quality.