Over a couple of days I have noticed unusual behavior in one of my young tosai. The fish was not swimming much, taking longer rests on the bottom of the pond. I observe it for a few days, but could't find an answer, when I finally realized that it had something to do with water pH.
After checking pH, I was astounded to find that it had dropped to 6.6 - 6.8 from its usual 8.0 - 8.3. This is what I was so afraid of for some time, reading the stories how everyone will go through one of these pH drops and loose all the fish.
It has been a lot of work since the April spawn, as I have being occupied with rasing the young. I lowered my guards and wasn't taking pH readings often enough, thinking that the water quality was always good, since I use bio filter and perform weekly 90% water changes.
With the addition of the spawn, the bio-load had increased and I neglected cleaning the filter from all the gunk for too long. As a result, I had my first bio-filter "malfunction" followed by a pH drop.
I spent today cleaning the filter and doing 100% water change. After the cleanup the pH went up to 7.7 - 7.8. I will be checking it regular and hope it will stabilize fast. The buffering capacity of my municipal water is good.
The lesson is learned - don't get distracted!