Problems with fish dying

For some reason a few says ago all the fish are breathing fast, laying on the sand, not really eating well, and dying. I tested the water and the salt and everything seems ok. I am not sure what to do. I increased the flow in the aquarium to get more O2 although I am not sure what went wrong.

Any ideas what to try next or just hope for the best.

 

What tests did you run?

 

Need to tell us more about your tank. Size, stocking, filtration, circulation (to include surface agitation, temp, etc.

 

also r u testing salt with a correctly calibrated refractometer or hydrometer... if your using a hydrometer your salinity could be way off unless the hydrometer has been checked by a refractometer and made adjustments

 

The tanks is 100 gallons with 7 fish left now from 10. I have a pelican 400 and 350 on the tank and two air wards. Also have two pumps on the side. The Temp is almost 80. PH is 7.4, amounia is 0, nitrites are o, and nitrates are 0.25. I am using a hydrometer and it has it in the middle of a good range. All my water I used comes from tab water but use Prime to make it safe. I have a 55gal plastic drum where I keep my salt water at the same conditions as the tank.

 

I think I know what went wrong but not sure. My Ph was 8.2 and I did a water change with ph of 7.2. I changed 30 gallons. Would that cause PH shock

 

absolutley, with rock and sand you prolly only have 75 or 80 gallons of true water volume, and 30 gallon waterchange would def throw your ph off...

i would HIGHLYYYYYYYYYYYYYYY advice you getting a refractometer or take your hydrometer once a month to a LFS and have them calibrate it to their refractometer and put a mark on yours...

the majority of hydrometers are .005 off (1.021 on a hydrometer reading would put your tanks salt at 1.026)

 

I'm not sure what a pelican 400 and 350 are but it sounds like and oxygen issue. Just adding flow is not enough, you need to point the powerheads at the surface to get aggitation. How large are the fish and what type? Do you have a lid on your tank? a skimmer?

 

The more I read the more I am convince it is PH. Good point, my 100 with sand and rock is really 80. The pumps are pointed up so there is a lot of water movement. The pelican 400 does 90 gall per hour and the 350 does 75. I do plan replacing those with a sump

 

pelican, do you mean penguin filters?

secondly you said you use tab water? im assuiming you mean tap water, next question are you on a well or city water?
You shouldnt be using prime to neutralize your tap water. Prime doesnt make the ammonia go away but puts it in a temporary form which may be building up in your tank.

Tap water contains tons of bad stuff that can leach into your aquarium.

Also no mention of protein skimmer, this will be your best friend for cleaning water.

You should slow down if you already have ten fish, lost 3 al;ready and do not own a skimmer yet, to help remove the waste.