is how you are achieving that mark?
Not sure what you mean exactly but...
I measure with an API liquid kit (just in case thats what you meant...lol)
I'm using a small HOB
power filter, the cartridge had been in there for a few months. Today I removed the cartridge but left the bio- floss insert thing.
Also a sponge filter which has been running to about a month.
I'm also suspect of using display water for PWC
's. I made sure it wasn't full of the usual bad stuff but perhaps the trace elements and buffers are used up.
I have new water mixed and aging for a PWC