The Estimative index is a simple method to dose nutrients for any tank without test kits. In a nut shell, the aquarist doses frequently to prevent anything from running out (plant deficiency)
Originally known as Poor Man's Dupla Drops it was created by Paul Sears and Kevin Conlin in 1996 as a method to supply the plants in the aquarium with all the necessary nutrients, but to restrict phosphate as a means to control algae.
The system which we refer to as Perpetual Preservation System (PPS) took many years in the making and many years of experimentation to fine tune, to document and to understand why some aspects worked and why some didn’t. We have developed two PPS systems to match every aquarium needs and personal preference.
This method was made popular by Diana Walstad, author of the book 'ECOLOGY of the PLANTED AQUARIUM'