Silica Sand causing tank deaths?

[freshfishies]

Hey all!
I'm suddenly having daily deaths in my planted tank the past few days, and I'm starting to wonder what the &%$ is going on!
Tank tests: PH 7.2, Ammonia 0, Nitrite 0, Nitrate between 5.0-10...the same it's always been the past 2 years.
The only thing I have changed in the tank recently, is that we added a bunch of very fine grade pond filter silica sand. We did that about 2 weeks ago.
Non of the fish are aggressive enough to be picking them off, and they are dying in small groups.
They aren't showing much as for signs of stress, except a couple are sort of greying, turning pale.
It's not a high tech tank, no co2, or anything fancy. I use under gravel tablets and liquid ferts, which has been working great for what we need for now.

Any suggestions on what could be causing this plague?
The only thing I can think of is the sand is causing some kind of problem now? I dunno *shrugs* Please help! 

Thanks!
Jazz

[Nerine]

the only way the sand would be an issue if it were contaminated? did you buy it from a pool store?? we just bought mermaid pool sand and no issues...

(plus i've been running their sand in my 55 for about 5 years)

when you added the sand did you clean filter out too? maybe the tank is re-cycling?

keep in mind the city is doing extra dosing of chemical due to the sewage spill offs and everything else they have had happen!!

hoping you dont have any more losses...

[morrom]

Hello

I have been having similar issues in my 12G, every thing seems health water is fine. The tank has been running for 6 months now, no major changes but getting odd deaths. The fish normally stops eatting then starts resting on the bottom of the tank, when swimming it dosnt look right very labor intensive. Then in a few days they die .

Trevor

[magnosis]

I think Nerine is right; maybe your sand was contaminated, and you're dealing with a bacterial infection of sorts ?

Correct me if I'm wrong, but I'm pretty sure Melafix can't hurt.

Thus I would suggest a full Melafix treatment (1 tsp / 10g / day / 7 days) and see if that helps.  Don't take my word on it though -- I'm definitely no expert in saving ill fish >.<

[freshfishies]

Thanks for the replies and pms guys!
I actually think it was the water. The plague seems to be gone now (leaving in it's wake a total death count of 20) 
I blamed the sand cause that's all I could think of, but I had rinsed it before putting it in, and the fish were all fine with it for 2 weeks.
For the past couple years I have been doing almost 50% water changes every week or so, but I think with the heat & humidity the city ups the chemical use or something like that right? Someone suggested to me that it could have been shock from the water change, which would make sense.
So I put in my uv sterilizer (it always seems to help clear up any infections or bacteria problems really quickly), and dropped in some more prime for kicks.
Hopefully it's all done with now. The remaining crowd seems to be going back to normal behaviors & colors again.
Cross your fingers!

[magnosis]

Glad to hear the good news 

[Nerine]

crossing fingers!