[Tiger15]

1.03 mg/liter copper is lethal (4 day LD50 or 50% died off in 4 days) to shrimp according to this study.

https://research.nhm.org/pdfs/27732/27732.pdf

Since your provider reported 1.3 copper and you do only 10% WC, copper in your source water is below the lethal level for shrimp. However, if you have copper plumbing, it may add more copper to your tap water to lethal level. In addition to copper, your plumbing may use zinc alloy solder that leak zinc to your tap that can harm shrimp. You don’t know until you test the water out of your faucet.

Are you sure you read your provider test reports right. 1.3 sounds high as it is EPA maximum contamination goal for human consumption that you may have mistaken as the actual measured level.

https://www.wqa.org/Portals/0/Technical/Technical Fact Sheets/2015_Copper.pdf

and

 

[Tiger15]

You should look under the 3rd column Results. You have 13 ppb lead and 0.38 ppm copper, both below mcl of 15 and 1.3 for human consumption. What come out from your faucet can be higher. I think new houses can have copper plumbing too as there is no ban. Your hot water heater likely has copper tank and/or plumbing. Metals in new houses are actually higher due to new piping that has not been thoroughly flushed. I don’t know how sensitive is API test kit, but make sure it is capable of detecting below the thrshold limit of 1.03 ppm. The most reliable test results are sample you send to lab that measure a long list of organic and inorganic contaminants at a small cost.

 

[Tiger15]

Can you look and see if you have copper plumbing, maybe where the water line or meter enters your home?

Another thing to try is to let your tap (faucet) run for 3-5 minutes and then use the water for water changes. Sometimes water setting in the pipes, especially newer copper ones, haven't built up the coating inside that normally reduces the amount of copper leaching.

There is copper plumbing more or less extensive in every household. Your water heater, faucet connectors, all or part of your piping can be copper or copper alloy. My old house has all copper piping and zinc or lead solder joints, but the plumbing is so aged that probably very little metals are leaching out.

That said, I never use hot water for drinking or cooking as hot water dissolve more metals. I don’t take first flush water for drinking when I return home from few days absence. Let it flushed for 3-5 min before using, longer if you have newer plumbing.

I don’t know if my tap has enough copper or zinc to kill shrimp as I never replace shrimp tank water directly from tap. Rather, I use the water from my big fish tank to replace the shrimp tank water after doing WC in both tanks so in a way using tap water indirectly. I use Prime to condition tap water in the big tank which binds heavy metals. The bound metals will precipitate out or uptake by plants in the big tank, so the left over water is safe for the shrimp. I am not sure whether Priming tap water directly in the shrimp tank is permanent or reversible when the pH drops.