I have the magic fish, I have the plant, I have better food, yet it seems like none of this does any good, and my fish get sick all the time.

What good is the magic fish and plant and better food if the fish are still gonna get sick all the time?

Seems like every time I re-enter the game, there are a couple of sick fish.

How about this? U tell me the answers and ill try to help u.
1. What plant/s u hav?
2. What magic fish u hav?
3. Do u hav al the upgraded food?
4.What is ur speed?

And any other info u hav!
Hope i can help u!

I didn't post details because I didn't want to spoil it, but I have:

The plant of curing from Isola
Magic fish of curing
Magic fish of health
I am fully upgraded on the food.
In fact, I have every upgrade possible (all the checkmarks are checked).

I have 6 out of 7 magic fish. Just missing #1.

Been playing for 525 hours.

Game speed is normal.

ok maybe u say how much money u have. If u hav more than $5000, then u may buy the fish vitamins that costs $180 each.
Then if there are any sick fish they should be fine for quite a while cos' the red liquid make them stronger and stronger.(of course u still need to cure them)
And since u said u have all mage fish except one, u should be able to thrive soon. Anyway u didnt say what kind of fish/fishes are sick often.
Is it the magic fishes/normal fish?

My fish tend to get sick more frequently as I progress through the game.

Watch how often you feed your fish. Too much food makes them sick especially as now you have researched the fish food, you don't need to feed them so often. It's easy to forget and feed them anyway!

The fish medicine isn't expensive although it is irritating to keep having to cure your fish. For very sick fish (health in red area) boost their health with vitamins before feeding the fish in your tank otherwise your recently cured fish may die.