Lost Tank Help!

I’m new to this hobby. 45 gal. tank with the following: 6 tiger barbs, 6 green barbs, 3 danios, 6 von rio barbs (wild caught), 3 Colombian tetras and 2 large Bn plecos. I did everything buy the book. Hard cycle with the 6 tigers. Water check (all water checks have been done by a couple of reputable stores) and added more fish. Did this several more times and then my little fish family was complete. I topped off my tank during this time as it evaporated a little, always treating the water with Stress Coat. Then three days ago I vacuumed my gravel and replaced about 20%of the water with water treated a week before with Stress Coat and Neutral Regulator (it sat for a week). Immediately one von rio starting flopping around. Call d the store. Added fish salt and upped heat to 80 and turned off the light. In the morning 4 more von Rios gone. As of this evening all my fish are dead except 2 barbs, the danios, one Pleco and 2 columbian tetras. ☹️ And by morning they’ll all be gone. I did everything right (I thought). I was patient and tested the water faithfully. Everyone got along (seriously). And then the water change. It’s disheartening as I don’t know what I did wrong and how to fix it. My 10 gal. tank with my Betta got the same water change (out of a different bucket, but same tap and treatment) and he’s fine

Oh, I took water sample in this afternoon and ph was really high. He sold me some treated water and I did a 10% water change. I guess too late. My ph was ok yesterday

 

Bummer sorry, get some Seachem Prime for future use. Better than Stress Coat as it detoxifies ammonia temporarily also.

 

Thanks for your tip.

 

pH usually isn't a culprit for fish deaths. Usually pH stays the same and shouldn't really fluctuate.

Do you know what the ammonia, nitrites and nitrate levels are?

10% amd 20% water changes seems rather small in my opinion, especially after multiple fish deaths.

Does your tap water have unusually high pH levels?

I ask because you said you treated your water with Stress Coat and a pH regulator and let it sit for a week before putting it in the tank.

Also, why does the water sit for a week?

I fill a bucket up, treat it with dechlorinator, then add it to my tanks.

On my larger 75 gallon tank, I drain it half way and then turn off the filters. I dose my dechlorinator straight into the tank then refill it with a hose hooked up to my faucet.

Never had a problem with that method.

 

Before I go into detail as to what I think happened I have to ask if this was the first water change you have done on this tank? How long has it been set up?

I am thinking you were given some very bad advice but we can help you start over.