Water changes

[reef-nut]

What is the best water to use for water changes? Is tap the worst? What does tap do besides algae? I noticed when I use RO or distilled I always had to adjust my ph.

 

[ZOABOY]

Ro/di...

 

[Russellaqua]

I use RO water. In most cases DI isn't necessary. Depending on where your water comes from it may already be very alkaline and this can cause a high pH when using salt mixes. Tap water is the worst because it allows any and all contaminants into your tank. Since marine life is used to very "clean" water with the exception of the compounds in salt mixes, they can suffer due to excess of other metals like lead, etc.

 

[reef-nut]

Does RO lower PH?

 

[saltwaternewb]

RO/DI>Distilled>Tap

 

[Russellaqua]

RO shouldn't lower pH. It should come out of the unit at near neutral pH of 7, but interactions with the current atmospheric pressure of CO2 (10^-3.5 atm) will eventually lower the pH to 5.4. This is unavoidable and will happen with DI as well. The CO2 interacts with the water to form carbonic acid, which then breaks into H+ and HCO3- (bicarbonate ion.) This is the same ion that dominates in nearly all natural waters, including seawater, except for very acidic or very alkaline water.

 

[J. Montgomery]

IIRC, from what I've read from Randy (RC's Chem. Forum), the pH of RO/DI water is meaningless b/c the majority of ions have been stripped from the water.

If your pH is off after you've made fresh saltwater, rather than accusing the water, I'd suspect the . . .
- pH measurement
- salt
- salinity measurement