Large water changes timings


Plant Guru Team
Lifetime Member
Sep 23, 2007
South Florida

Just an FYI on how long to perform a %50 WC on a 180 gal using a 500 gph Mag drive pump with 1/2 outlet and and then a 3/4" ID return hose just using the tap flow:

Drain time 90-100 gallons 10 minutes.
Fill time 90-100 gallons 18-20 minutes.

I just now did about a %75-80 and took 45 minutes total to drain and fill. All ferts, pruning, cleaning, etc done during that time. I use 2-3 x Prime dosage.....

I place a sponge on the drain pump and then place it on the substrate so that the intake of the pump will go dry if below bottom 1/3 of tank level, which is how I just did a 75 instead of 50 as I was typing this lol...

I know not everyone has a spare 500 gph laying around, but a smaller pump would work as well, just slower. For large or multiple tanks, I think a pump for this purpose is a good investment, esp with EI.

Maybe you can use the pump for your c02 reactor if you use one or it can be easily removed/reused for this purpose.

Just to demo how little time these tasks can take with some tools/automation...

The benefits to my fish/plants has been enormous!

I would love to have it setup so I could just hit a switch, but maybe some day when/if I own my own place :)