Fishing Pen

Fishing Pen
Do i need solution 4 and 7 to calibrate ph pen for marine fish tank?

I have ph pen that i need to calibrate. i only have solution 7 but the readings still seem to be off. do i need solution 4 as well

If you are using it on freshwater , then just using 7 is fine. You always want to calibrate to a level you will be testing at. would calibrating at 2 be better, sure it would. Being off by .3% is really not that big a deal. Ideally you would want to calbirate using 7 and 10. That way your target is right in the middle.

Mini Fishing Rod Pen