Lowering salinity

hm189 · Nov 11, 2024

I'm currently doing a fishless cycle on my first saltwater tank. Apparently my refractometer was way off and I realized the water in my tank is at 40 ppt. It's a 20 gallon tank but only about 14 gallons of actual water volume because I have a lot of hardscape. How many gallons should I take out and replace with RODI water?

Jay Hemdal · Nov 11, 2024

hm189 said:
I'm currently doing a fishless cycle on my first saltwater tank. Apparently my refractometer was way off and I realized the water in my tank is at 40 ppt. It's a 20 gallon tank but only about 14 gallons of actual water volume because I have a lot of hardscape. How many gallons should I take out and replace with RODI water?

Welcome to Reef2Reef!

One of our fish medics created a calculator (2nd tab on this spreadsheet I think):

Fish Disease Calculators

During the course of caring for our fish, we often need to make calculations regarding several recommended treatment options. Most water quality maintenance steps are supported by calculations provided in the "Reef Chemistry by Randy Holmes Farley" forum. Taking it a step further, additional...

www.reef2reef.com

However, I find it complicated to use. If the tank has no animals in it, you can just eyeball it: 40 ppt is about 5 ppt to high. I think you can remove 1 3/4 gallons and replace it with RO water - that should get you pretty close.

fishywishy · Nov 11, 2024

If you there’s nothing in your tank just remove saltwater and add RO water until you get to where you want it.

If you’re worried about it restarting your cycle (which it wont) you can just remove and add water every 30 minutes or so until you get where you want.