Osmocote Root Tabs - Ammonia?
A few days ago I added 10 x Osmocote root tabs to my 125G tank, the tank has been set up for about a month but was an upgrade from a 55G. So everything transferred over (except the original substrate). Over the last few days I have started losing an alarming number of fish, at the moment 3 x angel fish and at this point I believe 10-12 Corydoras.
I took a water sample to an LFS, as the API Liquid kits I have on hand are I suspect out of date. They indicated that ammonia was showing up, not in high levels, but enough to be concerned. I should have asked them what the PPM was.... The fish can be completely fine one day, then start acting listless, ignoring food and then dead by next morning. The corydoras I don't see any symptoms, likely due to them being hidden in plants, under wood etc.
Ruling out any sickness, I did some searching and found more than one instance of Osmocote tabs causing an ammonia spike. I have black diamond sand in the tank, at about 2.5" of depth. I pushed the root tabs in to what I thought was a sufficient depth, but it appears I may not have done so. Having said all that, the tabs will have been in the tank for 4 (maybe 5) days now, so likely the casing has dissolved. I have been carrying out daily 50%+ water changes, but am wondering if it is the Osmocote (and not an illness) causing a spike, how long should I expect it to continue with 10 tabs in the tank? I realize ultimately the beneficial bacteria should multiply enough to handle it, but in the meantime is it a case of daily testing and water changes until I read 0 ammonia and simply hope it is not too much longer.
The strange thing is that I have a few tetras in the tank and have not lost a single one. The angels were new, so possibly stress with the ammonia is what ultimately killed them? and I am assuming corys are taking the brunt due to being low down in the tank where I assume ammonia is being released from the tabs.
I have read that the tabs should last 3-4 months, in future how many should I add to a 125G that is moderately planted?