"miskairal" wrote in message u...
This is normal and pH of rainwater is low because it lacks of buffers
which could neutralize CO2 dissolved in it. You should not be worried with
pH of rainwater and do not even measure it - same for pH of RO water...
What is important, is pH of sal****er, after mixing it and before putting
it to the tank.

But wouldn't making my salt water mix out of the rain water cause the pH
to be lower than using the creek water? I have freshwater fish as well
which is why I know the pH of those waters.

Are we talking about creek water directly or after reverse osmosis filter ?
First one would have more buffers, so pH might be slightly higher than
if rainwater was used. Second would be almost the same, since RO
filtration removes almost all buffers, like evaporation does for rainwater.
Think of rainwater as demineralized water, similar to distilled and deionized.

So you prooved only one salt mix does not contain phosphates and use
this one.

Yep and I will just have to buy more coral to soak up the calcium
(after I replace the MH tubes).

Good idea :-)