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Could be a combination of the salt (sand if recently added) as well as the low
GPH in the tank. The whisper 60 is only 270
GPH rating when empty. Once it has media, the flow will be reduced a fair amount. Do you have additional
PH in the tank as well?
Good water rotation starts at 6x rotation per hour and that is considered on the low side. Ideally you will have to determine the total
GPH based on the type of tank you will end up having but for the most part you should try bringing that up to 400+
GPH.
The low
ph could again be from the salt but low
GPH and possibley having the tank covered would affect it as well.
Any additional info you could provide about the set up would help.
Cheers
Steve