Radion XR15W G4 PRO

[NanoReefMinimalist]

Anyone knows how to calculate PAR at different depth?

[ReefObsessed]

Unfortunately, the only way to accurately measure PAR is with a PAR meter. One of your best (& cheapest) options is this: 

 

https://www.bulkreefsupply.com/seneye-reef-monitor.html

 

It not only measures PAR, but also keeps an eye on Ammonia and pH.

 

HTH

[Segalplayer]

Ugh is there any place to rent one...I don’t reallt want to own one for one-2 time use 

[Okinawa_Reefer]

BRS has some very in depth videos that will show you various PAR reading at different depths on different size tanks. They show the readings at 100% levels and also the readings with the light set to the AB Spectrum. Taking your own PAR readings would be best, but that video could get you pretty close.