Do you know if your guppies were raised in the Far East? Evidentally they add salt at an irregular, but irresponsible level to their ponds/ tanks.

You might check with the shop for origins. Also ask if they have had similar problems with the guppies. Ask what they are doing for their guppies if they have been having problems.

Please see

Diaries
Mollies, Salt and Asian Imports    
Care Tips
By unclescott [
from the minerology department,
Posted on Sat Jan 31st, 2004 at 15:06:50 PST

The often fatal shock which East Asian (Singapore, Thailand, Malaysia...) guppies go through when quickly moved from their super salty water to regular hard water in the US has caused some shops to quite selling them.

I have heard that Dutch aquarists will catch rainwater as a preferred aquarium water. If your guppies have an Asian origin it may be that you not only want to add your dose of cichlid salts (or Ro Right ...) but also a significant quantity of sodium chloride (but not table salt with silicates which keep it pouring, but also coat gills) to your water.

If your fish have been acclimated to low mineral water after having been shipped in that water with a high salt concentration, you may not want to suddenly shift them to another stressful change into a new water chemistry. But that may explain the problems.

I think you know to do this, but for those lurking, there are some careful steps designed to keep the stress and shock levels at a minimum while adjusting new fish to your tank.

To make their acclimation as smooth as possible:

1. Pour most of the shop water out of the fish bag or leave the fish in a jar with just a little of the shop water.

2. Put a little tank water in the bag (or covered jar) - as much as the water already in the bag.

3. Wait 20-30 minutes, pour some water out,

4. Again put about as much tank water in the bag as was there and wait another 20-30 minutes. (Go check Guppylog.)

(They should be pretty used to the new water chemistry by now.)

5. Pour ALL the water though a net into a garbage bucket. Or if you have to, put you hand over the bag opening and slowly release all the shop/bag water into a bucket. (The fish may bring some disease organisms into the tank on their bodies, but why pour so many more in with the water?)

6. Gently drop your fish, minus any water, into their quarantine tank or new home.

Tough fish like guppies can be acclimated in 30-60 minutes. Touchy marine fish may take half a day.