Using distilled water for a water change

[PrettyFishies]

I'm about to do my first water change after 7 days and am concerned about the PH. We filled the tank with Poland Spring which has a PH of 8. I'm assuming distilled water has a PH of 7... Is that right? And the other thing I assumed about distilled is that it is tripped of all trace elements and nutrients... Is that true? And if so, do I need to dose the changed water with everything or wait till it gets in the tank, test then dose.

 

[An t-iasg]

What is the pH of your tap water? Let a glass sit out overnight and then test the pH. Is there a reason you don't want to use tap? For a planted tank, if you're going to inject CO2, the KH value is important too. The KH should be at least 3 to prevent pH swings if you're going to use CO2, either pressurized or DIY.

Distilled water isn't good to use in an aquarium because it will not contain enough minerals to act as a buffer to stabilize the pH. Distilled pH is usually lower than 7.0 because it doesn't have the buffers necessary to hold a good KH or stabilize a pH. Since the buffers are low or absent, the amount of CO2 that gets into the water from the air is enough to drop the pH. There are additives for buffering distilled water - RO Right is one product, from Kent, I believe - but before you go to that trouble, do some pH and KH tests on your tap water if you haven't already.

I just did some tests on my distilled water (I use it in the iron, not for the fish!)
KH: 1
pH: 6.4

 

[PrettyFishies]

We don't even drink the tap water without filtering it - it has a bad odor...

How would I even know if it is bad for the plants and fish?

I see now that I should not have used the distilled water - thankfully, the water parameters are fine and I will just get mineral water next time...

 

[Simpte]

Using SOME distillied (R.O. etc..) water is fine. I wouldn't use more than 60% of your tanks total volume though. I use R.O. water almost exclusively but keep at least 20% tap in my tanks as we have very hard water here and I keep S.A. dwarf cichlids and other softwater species. The key is finding a good mix of both to achieve the parameters you want.

 

[Purrbox]

When using RO or Distilled water you will need to add back in the minerals and buffers with a product like RO Right, unless you mix it with at least 50% tap water. Your standard ferts won't be enough, because they assume that the buffers and certain trace ferts are already going to be present in your water.

I was mixing 33% RO with 66% Tap water to help soften up my liquid rock. Thankfully we have much better tap water after the move and I am back to using 100% tap water. Much easier and less expensive.

 

[Lonewolfblue]

I agree with Purrbox, if using distilled water, it should be mixed with tap to maintain some of the buffering ability. The most I'd do is 50/50, but that's just my opinion. As for mineral water, I've heard a lot of rumors on that as well. If you don't want to use the tap, then about the only thing left is going to the store and getting just plain drinking water. Not distilled, and not mineral water. Get a small 20oz bottle of drinking water and test it for ph as well as kh and gh. I may try that just for future reference, as our water here is just fine. I see them at Safeway here, just the Safeway brand of drinking water, not the purified water.

 

[BillD]

Because the tap water tastes poor doesn't mean it is unsuitable for fish. If the tap water is safe to drink (regardless of taste) it should be fine. You can add a canister water filter, containg a carbon filter element, that will remove most of the chlorine and bad taste. They are available at places such as hardware stores and home Depot. If you have to buy and lug water to do water changes, it will soon become a chore that will lead to neglecting the maintenance, or quitting the hobby.

 

[An t-iasg]

Because the tap water tastes poor doesn't mean it is unsuitable for fish. If the tap water is safe to drink (regardless of taste) it should be fine.

Good point - I don't drink our tap water either; I buy bottled water for drinking, but the aquariums all have 100% tap water and the fish and plants are doing very well.

 

[Ryehard]

I have to filter my water because unfortunately the parameters of it change constantly out of the tap when my town changes water sources (the filter is built into my faucet so it's easy and relatively cheap). The only reason I use RO water is to replace evaporation between PWC's.