How do I make an object detect when it collides with another object of the same type?

Im making a physics sandbox game and to optimize the performance i want to make so acumulating objects of the same type, instead of piling up one gets destroyed and the other one gets bigger (something like how Agar.io works for example)

any ideas in how can i solve it so it works?

pick one with instance 0 and the other with instance 1.

Otherwise you can't tell them apart. So use pick by instance.

make 2 families and put the Water object in both

Then compare families but skip the same objects...

sort of like this:

although here I am looping through, in your case you just need the one trigger