[Dave71]

I am going to suggest a relatively simple approach, that does not require scales etc...

For your tablet you can treat approx. 190 gallons of water. Basically half the volume of water that the larger tablet treats.

Now this is not an exact dosing science, so some may say just use the whole thing.

But lets suppose you want to be more precise.

Steps:

1. Crush the pill into poweder
2. Get a small measuring device. I like Salifert Test spoons for this.
3. Determine the number of spoons of powder you have created from the crushed pill.
4. Divide 190 by the number of spoons. You now have the gallon per spoon measurement.
5. Dose with the number of spoons it takes you to get to 130 Gallons.

Just my approach.