This tank is just one in thirty five that we look after in schools throughout the area and it's located in a small community where there is a single large well that feeds the entire town. We are raising Coho Salmon eggs to the fry stage. The eggs seem to thrive in the well water and we usually have 95% survival. As soon as they are ~2-3 days from hatch, however; we have to have water trucked in from a neighboring community or they all seem to die off.
I have herd of some communities where the water being pumped from great depths gets super saturated with gas and has to be misted to release the gas before being used. We have tried this here but we still get high mortality rates so there must be something else going on.
Tom, I've read your posts on the planted tank forum, and the "Venturi" system seems like it might work pretty well so long as that is the problem we're dealing with. It certainly seems like a good idea for my own tanks!
I should be out there sometime within the month so I'll take the LaMotte kit and get some exact readings that should clarify things (at least for me).
Thanks much everyone!
Could be degassing of O2 also, but CO2 is common, CaCO3 geology adds lots of CO2 to well water, O2 can be at high levels, particularly if cold and then warmed up some.
I'd try a subsample, degas it it good and then try on the 2-3 day old fry, eggs and hatching should be okay, but once they develop more, that's where there's all sorts of issues.
I'd run it through activated carbon and degas it with vigorous aeration/surface turnover in a holding tank. That would take care of gas issues and any unknown organics. Try at a small scale, see if you get the same results, then scale up, better than trucking water in.
You can also look at the development stage of the fry also in more detail at the 1-3 days stages. Might find answers to the issue/s there.
Since there's a lot of fry to be had, and the issue oif trucking water is large, I'd work from a practical standpoint also, try a subsmaple and degas the water and see. Then AC if that does not work.