Top off with Mixed or RO water?

[jandc805]

I have read books that say to top off your tank as needed with Fresh RO water. Would it be ok to top off with extra mixed water you have laying around from a previous water change? Or should that water be dumped after some time?

 

[mfdrookie516]

No, you'll raise the SG if you top off with SW. When water evaporates, that's all the evaporates... everything else stays behind. You're replacing the water to keep the SG the same.

 

[jandc805]

It seemed when I was cycling and I started off at 1.026 after 3 weeks of topping off with RO water I ended up at 1.024. What would cause that?

 

[ccCapt]

What are you using to measure your salinity? Hydrometer or refractometer?

 

[jandc805]

I use a refractometer

 

[SeanMonster]

Stupid question here: How often does a refractometer need to be calibrated? Only asking because I don't currently own one.