I have an Eclipse 12 gallon acrylic tank (which I'm very happy with). I started the tank at the end of April with a couple of zebra danios (had read they were good fish for cycling tanks as they are hardy. Indeed they are ... they survived the cycling process and grew a good bit during it. I stayed on top of water testing and cleaning/water changes, and have seen ammonia and nitrite both go up and come back down again. For at least a few weeks now ammonia and nitrite have been zero, and nitrate very low. I've been changing ~25% of the water once a week or so.
So it seemed a reasonable time to add more fish. I should state that my goal is a community tank. Picked up another danio since odd numbers are supposed to be better (the first two did a bit of fin nipping), a male guppy and a plec to help with algae control.
Sadly the pretty little guppy expired after 24 hours, and the plec about a week later. The new danio seems to be doing fine, though.
I took the guppy back to the store along with a water sample, they told me their test picked up "some" ammonia and my pH was high. This was a surprise to me since my test kit has been saying ammonia was zero and pH around 7.2. All the same I picked up an in-tank ammonia monitor and a separate pH test for confirmation. Neither the ammonia monitor (which is supposedly even more sensitive than the test strips I'm using) or my tests show any ammonia, and pet store guy wasn't exactly being precise when doing the tests so I don't believe I have an ammonia problem.
My pH, however, is definitely high. The Mardel test strip continues to say it's around 7, it is clearly wrong. Turns out my local water utility is raising the pH to something like 8.6 to prevent corrosion in the lines. So I'm wondering if high pH alone could explain the death of the guppy and the plec.
A few questions - anybody else had a bad experience with Mardel test strips? (I have their "master test kit".) Should I pitch them and get a test tube/reagent style set? What about the SeaChem ammonia alert in-tank monitor I'm using now?
As far as pH, I have figured out by experiment that 16 drops/gallon of 5% acidity white vinegar will bring my tap water's pH down to neutral. I plan to do this to new water as I replace water 25% at a time, and so gradually bring my pH back down to something more reasonable before trying again with more fish. Any thoughts?
Edit: a couple more bits of info - the tank receives a fair amount of indirect natural sunlight. The tank has a compact fluorescent toplight that is on probably 6 hours a day. There are no living plants in the tank. Food is TetraMin tropical crisps.