sorry to hear that Bolton fan, I kept fish for years and you have to be careful with their food.
were they swimming strangely, that is a classic sign of Swim Bladder 
- Have you changed their diet?
- changes in diet and increase in protein can cause constipation and digestive problems. Common example is Swim Bladder
Swim Bladder Disorder refers to issues affecting the swim bladder, rather than a single disease. Although most commonly seen in Goldfish and Bettas, it can strike virtually any species of fish. In this disorder, the swim bladder does not function normally due to disease, physical defects, or mechanical / environmental factors. Affected fish will exhibit problems with buoyancy. Interestingly enough, not all fish possess a swim bladder, most notably sharks and rays.
Symptoms
- Fish sinks to the bottom, struggles to rise up
- Fish floats to the top, often upside-down
- Swims with tail higher than head (Note: this is normal in headstanders)
- Swollen belly
- Fish may have curved spine
Fish suffering from Swim Bladder Disorder exhibit a variety of symptoms that primarily involve buoyancy, including: floating upside down, sinking to the bottom of the tank, standing on their head, or struggling to maintain a normal upright position.
Other physical signs such as a distended belly or curved back may also be present. Affected fish may eat normally, or have no appetite at all. If severe buoyancy problems exist, the fish may not be able feed normally or even reach the surface of the water.
Cause
- Compression from surrounding organs, such as:
Enlarged stomach from overeating, or gulping too much air
Enlarged intestine, due to constipation
Enlarged liver, generally due to fatty deposits
Enlarged kidney, generally due to cysts
Egg impaction in females - Bacterial or parasitic infection
- Mechanical injury from fall or other hard blow
- Birth defect
poor wee fish
