Is my water Stable?

[FishGuru]

Hi, when I combine 4 gallons of DI water with 1 gallon of tap water, I get a pH of 6.5, kH of 3.5, and GH of 4.5. Is this stable enough to prevent pH crash? Thanks!

[RandalB]

Depends on how often you change the water. The kH gets used up by acids from biological processes and will drop eventually. My water is kH 6 and almost never drops.

RandalB

[knobby]

is this before/after you add it to fish tank?

before/after it is aged alittle?

if those are your measurements immediately after mixing it then I would guess no you water is not stable enuff. After you add it to the tank the biological processes will usually drop the ph some. How much depends on your kh mainly tho....

[Nightowl]

Yes, when concerned about PH crash its the KH level that you want to keep an eye on. If you can maintain a KH of 4 you will better prevent a crash. At 3.5, you don't have far to go to have unstable water. Under 50 ppm (just under 3 degrees)KH,water is VERY unstable PH -wise, and Ph can shift rapidly in either direction: lower from organic acids, higher if you add too much buffer.
You 're currently using 20% tap water with the DI water. Try 40% and see what you get...A GH of 6 and a KH of 5 is not terribly hard water to use for water changes and would be more stable.Plus, these ions get used up regularly by processes going on in the tank, so where your water hardness ends up might be right on the money.
good luck! J.T.