We were casualty free for many weeks straight but the streak is finally broken. One CRS died a few days ago and a cory cat died yesterday. Who knows why the CRS died. But, the cory cat was suffering from signs of gill burns. Few days before he died, he was hitting the surface for air quite a bit and totally lost appetite. Then, I saw the gills were turning red.
Did a water test and found the PH to be around 8 but everything else is in zero range. Dunno why the PH is so high. Previous water tests had the PH under 7. So, I ordered a PH meter off amazon which took a few days to arrive with prime. In the mean time, I did a water change and found that the small rocks I bought at Joanne's that I used at the bottom of the tank is actually leaching lime. So, I removed as many of the rocks as I could without disturbing the rest of the tank which is about 3 hand full.
Finally got the meter yesterday night and used it this morning to find my PH is actually at 6.5. So, it seems my water parameter is fine. I also got the Seachem ammonia alert, and it says my water is "safe" (yes, I've read this product is iffy but only using it to confirm my other tests). So, it's a mystery why the cory cat got gill burn.
Anyways I got a new lens, Rokinon 85mm 1.4. Here's a FTS with the new lens. Tele is too high with the 1.5x crop factor on the D90, so parts of the tank is cropped. Here's a sample at f1.4: