Today when I tested my water I noticed something I'd never noticed before: my alkalinity reading is 40 ppm, which according to the tester description is too low. But my ph tests in the neutral range. I have never had a problem with the ph before and I don't remember the alkalinity ever testing badly but I am unsure. What exactly does the alkalinity mean? Is this very harmful?

Alkalinity is the buffering capacity of your water. Another name for this is KH or cabonate hardness. When carbonate hardness is high, then your water has a large capacity to absorb the acidic byproducts of the nitrogen cycle without your pH falling. When your carbonate hardness is low, even if your pH is in a neutral range, your water has less capacity to hold a steady pH. With alkalinity (or KH) of 40 you need to be on the lookout for a pH crash -- this is when the byproducts of the nitrogen cycle accumulate and all of a sudden your pH falls to 6.0 or below overnight. This can be very dangerous to your fish. Ways of bringing your KH up include: adding baking soda (a temporary solution), putting crushed coral in your filter, or adding a commercial buffer like Buff It Up (www.goldfishconnection.com) to your water.

Which method would you say is the best? If you use the baking soda or commercial buffer, do you have to add that every time you do a water change to keep it at the right level? Thanks for your help.

Baking soda raises the pH and crushed coral sustains it.

Buff it up does both and will usually sustain the pH for about a week(which is the longest you should go w/o a water change anyway).

What is your pH out of the tap and pH in the tank?

The ph for the tank water and the tap water is the same...it tests neutral, which is somewhere around 6.8 to 7.2 according to the test. I am aware that the testing strips are supposed to be inaccurate, but I bought these a long time ago and I don't really have the money right now to buy the other kind.

I wouldn't put a lot of stock in what old test strips are telling you. They aren't very accurate under the best of circumstances and age and exposure to even the tiniest bit of moisture will make them inaccurate. If you do in fact have low KH, then you would expect to see a lower pH in the tank a few days after a water change. Have you ever observed this phenomena?

No, but I don't remember specifically testing a few days after a water change...maybe I will test today or tomorrow and see what it says.

6.8 to 7.2 is a big range. The pH scale is not linear thus a point is 10X and 2 points is 100X. In another words, a 2 point drop means that your goldie's water just got 100X more acidic. A sudden drop of 2 points or more is what is referred to as a pH crash.

7.4 is the perfect pH for Goldies. You are better to err on the higher than lower, so IMO, 7.6 is probably the best as it gives that extra cushion of safety in case of a slight drop. 7.2 is OK but 6.8, combined with a low KH, is starting to get uncomfortably close to what I call that "pH crash waitin' to happen" zone.