Here is the situation:
I have a Fluval Edge tank that is fully cycled and has been set up for three months. If you want to see some pics of the tank for reference, you can view here: Nano tank build with pics
I have Flora Max substrate on the bottom, three rocks I found outside my home (extensively cleaned), African driftwood, xmas moss, chain sword plant, java fern, and I believe a plant called amazonicus. The rocks are basalt I believe and I tested them with vinegar to check against possible limestone composite makeups. The cycling process completed in less than a week and a half due to using seeded media and lots of live plants. Two golden white clouds have been in the tank since the cycling process completed. The presence of ammonia and nitrites have not been recorded in the tank for months.
About a month ago, I bought 2 crystal red shrimp, 1 bumble bee shrimp, and twelve painted fire reds. The CRS and BB were bout from a reputable LFS, while the PFR were bought from an online breeder. The PFR shrimp were all older full size adults to my dismay. Immediately, one of the largest (most mature) CRS shrimp died in my tank. In addition, the PFR shrimp have died off at a pace of about 2-3/week, resulting in two lone survivors. The BB and the other two CRS appear to be young and active as do the golden clouds and "Sassy" the snail. So now in total I have 2/3 CRS remaining 1/1 BB shrimp and 2/12 PFR Shrimp, which are supposed to be the most hardy.
Here are my tank parameters:
Nitrates: very low
PH: >7.6 ( cannot tell since my test only goes to 7.6)
At my home, we have a pretty advanced under the sink filtration unit for drinking water, consisting of multiple canisters. The water from the filtration unit tests comes out as: http://www.custompure.com/MB618-EB-style-P8.aspx
The regular Tap water tests the same except for a PH of 7.3. I have only used the filter water in my tank so I do not understand why the PH is so high? As a note, the driftwood was only placed into the tank a few weeks ago while the shrimp die off was already in progress.
What is causing the massive shrimp die off?
Old age? PH? Chemicals? I am stumped here because old age is unlikely to kill so many shrimp within a short interval, the high ph should affect crystal reds more than cherry reds and I doubt chemicals are in my tank.
My second problem is my high PH. Does anyone know why my PH is so high compared to my water source?
From what I have read online, basalt rock should not change the PH of the water at all, let alone over a point on the PH scale.
If anyone could help solve the mystery it would be great! I have no clue what my next step should be.