Lost Fish So Have Done Water Test. Please Advise!

[brads]

OK, My tank has been up and running now for 18 months, untill now I've had no problems.
Over the last four days I have lost 2 tiger barbs, 2 gouramis and 1 female sword tail.
I have just bought an API water test kit. weather or not there any good is would be nice to know.
Anyway these are my test results.

PH 6.0
Ammonia 0.25
Nitrite 0
Nitrate 0

After this find I took a sample to my LFS (MHA). My PH was the same on there test kit, which they explained is why I have lost fish.
So to get the PH back up they sold me something in a bag but I can't recall what it is called. It looks like white gravel of all shapes and sizes. They told me to put a table spoon worth into my filter, and it will dissovle over time and bring the Ph up.

I'm going to do a water change today. I usally change 36 liters a week (3 buckets). But should I do a much larger change?
Is the API test any good?
What do you guys advise to do?
After a water change how long should I leave it before doing another test?
See my sig

Cheers Brads

 

[CarbonDreams]

I would be more worried about the NH4 if I were you. If you have a ANY reading than that means your tank is going through a mini cycle. This probably was the culprit rather than the PH. Fish can adapt to different Ph, and it is really hard to change your Ph consistantly (depending on your water from your tap) More often or not, you will just simply send your tank on a ph rollercoaster which would harm the fish much more IMHO. As long as your PH is constant, it is ok if it is a little low.

To get rid of the NH4, test daily, and be prepaired to do one or two small changes daily until you are showing no more NH4.

 

[loachman]

I'd agree that the ammonia is a bigger issue.

CarbonDreams advice will work for ammonia control.

 

[brads]

Cheers for the replies. Could anyone anwser my other questions? also-
What would you class as Ph being a little low?
I have changed some of the media in my filter so that may explain the mini cycle!