Also since you have no substrate or filter why not remove the fish from the water to a new water holding container.
Clean the containers. Make sure to clean as to kill bacteria in the bacterial bloom. Super thoroughly rinse the containers.
New water and then start over.
disclaimer: No experience here with scientific experiment or why it needs to be done.
Adding the correct type of remineralizer for fish to more closely replicate natural water would be more beneficial for the fish, and they would be healthier.
Keeping fish in unsafe water parameters will make experimenting probably not accurate because fish will die from unsafe ammonia, nitrite and nitrate, ruining your experiment I would think.
The amount of food you are feeding is likely the problem as well. Reduce the amount of food added and how fast you add it. Just to the amount they can eat in a minute. Add some food let them finish eating it all then add a little more to they quantity of what an estimate of a normal feeding would be.
Then in relation to the salt added in the water this info popped up, might mean more for you.
The remineralizer additive has a good combination of ingredients necessary for osmoregulation.
Also the color of the food certainly could tint the water pink.
What are the ingredients of the food?