Oh you can spawn in water this hard but it is just more difficult. Heck Ive spawned in it but this a factor in the breeding of many fish species in my area. The water chemistry varies alot depending on where you live for sure. Ive done the numbers and a much more perfect spawn water would be a 50-50 split between my tap water and pure water. This change will take the fish days to adjust to so it has to be part of my conditioning process. Ial works but it takes days for the tannins to really start coming out and breakdown of matter so it needs to be added early before fish or mixed in as a concentrate. I like the tea because I control the strength with little variation.
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