Hi I am new to this forum, I found here about alum sulfate for clear water. I have bought 1 pallet of alum. sulfate aprox. 1 metric tonne.
How much should I apply my size of pond is 3.000.000 gallons of water.

Last year I emptied whole pond and removed almost all fish except grass carp, planned to buy sand to place all over the floor but weather was no good so I left it as it was. Then this year in march and april the water was really crystal clear at some point visibility was up to 6 feet, then because of the clear water I have got issues with algae. Algae made a water a little bit greener.
In that period I have put 100 trouts in the pond so they can catch frog eggs because we have always issues with frogs.
But in May we have noticed some of the european carp still remained in the lake (we thought it was young grass carp in Europe grass carps are not triploid), and since then as weather got warmer they started to dig in the pond trout and european carp, since then water started to be again muddy which I do not want, found a few weeks ago about alum sulfate, but could not find how much to put per liter/gallon.

At this point I am thinking of putting northern pike into the pond because european carp is still small it will eat it, and grass carp is big (i do not have issues with grass carp most of the day it's at the top of the water it's almost never at the bottom it behaves totally different, also one reason why emptied pond last year was because european carp almost dug trough our dam...).

So my question is when I throw alum sulfate is it one time application or it will last for some period ?

Here are pictures how it was before removing european carp and this same quality of water is now....


This is when the algae took control



This was when the water was perfectly clear...

Tarik, welcome to Pond Boss. You live in a beautiful place. I’ve never had to use alum so will defer to others.

Tarik - beautiful place! Sounds to me like your main issue is carp stirring the water up. Alum won't fix that.