If the pickerel was wild caught (by you) one of the best things to do, (after you get a test kit), would be to test its natural water to find out its nitrate content.
I test the rivers where I catch my fish I keep for pH and nitrate. And judge my water change routine (how often, and how much water is changed) according to those water parameters are, and wharoutine it takes to maintain that water .
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As you can see by my test results, pH hovers around 8, and nitrates are non-detectable.
So my water change schedule is 30-40%of my 300 gal system changed every other day to maintain the quality these fish have evolved to live in, in nature.
I discovered this routine would work, by experimenting with different schedules to see what held water quality at those natural levels.
One other thing I would caution about is the use of cyprinids like minnows and goldfish as live food.
Cyprinnids are notorious carriers of parasites that can cause disease, so weaning to safer food would go along way to keeping a fish safe.
All it takes is 1, like this Lernaea parasite on the dorsal of the tetra below.
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That parasite wiped out an entire QT tank of about a dozen tetras, before anti parasitic treatments wiped the Lernaea out.
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