Water chemistry questions GH KH PH

[cobrasnake2003]

Ok I have a few questions about my water hardness and PH. I just got back in the hobby and live in a town with hard water. I just purchased a typhoon III RO/DI unit and am planning on mixing my tap with the RO water to get a softer water. My PH is currently around 7.4-7.6 from the tap (API test kits suck for PH). Unfortunately in the tank it is hovering around 8.0. I am not sure what exactly is raising it and that will be one of my questions below. Anyways here are my params and a few questions I have. The tank is a 180 gallon with 2 magnum 350's, an AC110 and an aqua 25 watt UV sterilizer.

Tap
GH 16
KH 11
PH 7.4-7.6

Tank
GH 17
KH 10
PH 8.0

around 50/50 RO tap mix
GH 9
KH 7
PH same as tap

1. Is it ok to do the 50/50 mix and add it to the tank? I will be doing 20-25 gallons every few days to slowly change it
2. WIll the 50/50 mix have enough of the essential minerals for the fish and plants?
3. If I wanted to go say 60% RO and 40% tap would that be ok?
4. How exactly could I get the RO/ Tap mix PH down to say 6.5-7.0?
5. Any idea what could be spiking my tank PH? I think it may be the sand. It is all-star play sand. I did some research and quickrete makes it and on the MSDS sheet says limestone but don't know if it is enough to raise it that much. Here is the MSDS Link http://www.quikrete.com/PDFs/MSDS-B4-Playsand.pdf THe only other things in the tank are a few live plants, piece of driftwood, and a few pieces of tile cut in half for caves.

Thanks in advance for any info. It is greatly appreciated!!!

 

[duanes]

If it contains limestone, it will raise your pH.
What kind of fish? That is really the important question. And do you really need to worry about it.

 

[cobrasnake2003]

4 Red hi fin wolf fish. I am not concerned about the health as they can pretty much live anywhere. My concern is to mimic some water params at my old house back in 08 where 2 of my 6 paired off and showed signs of breeding. Unfortunately my girlfriend/wife got prego and went into full on nesting mode. The tank room was converted to a kids room. Pretty much got out of the hobby for a while. My params back then were PH 7.0, KH- 8, GH-9. I had malacaribus breed as well as gold piranha and RBs.