HELP! low ph

[chickenjohn]

Need help as im at a loss.
Im setting up my quarantine tank to cycle, last week I mixed some salt (Tropic Marin sea salt) and its ph was 6.8, this was tested on 2 test kitsand a ph meter.
I opened my other tub of salt and it read the same ph, I took sample to lfs to be tested and he got it to 7.0.
I ordered a couple of red sea blue bucket salt and drained tank and started again but when I checked ph again it was 7.0 on 2 tests and 7.1 on meter which has just been calibrated.
my tank is a basic 75 litre with only a fluval u3 internal filter and a powerhead in the tank and bare bottom.
Surely 3 tests and a lfs test cant be wrong but surely I cant be unlucky and have 4 tubs of salt with incredibly low ph,
Any ideas what could be going on?

 

[Uncle99]

Normal reading for a new mix
If DT is 7.8 or higher, don’t chase this number

 

[chickenjohn]

It is supposed to mix at 8.2 and 6.8 is not a normal reading.
when I used the blue bucket before when I had a fowlr tank it read 8.2 straight away.

 

[Uncle99]

Whats the PH of your Source water?
What's your ALK?

 

[chickenjohn]

Ph of ro water is 6
Alk 5.5 dkh (low which could explain low ph but opens another question, why is alk so low)
Cal 420
Mag 1200

 

[DaveK]

Because there is very little in it, ro/di water, before you mix your salt, often has what would seem to be abnormal pH readings. These can be ignored, but if it bothers you, you can use a small amount of baking soda to bring up the pH. Note the is for ro/di water before you mix salt in it.

Another thing to check is the container you are using to mix the salt in. Sometimes they can leach stuff that causes a problem.

I would agree that the pH your getting is very low. You will likely need to track this down by testing everything. One thing you can do is get one gallon of distilled water from the grocery store and mix that with the salt and test. That will show you if there is a problem with your source water. It is possible you have a problem with your ro/di unit.

Also note that most readings you make, other than pH is dependent upon the SG of the water. I highly recommend using a refractometer to measure SG. It's a lot more accurate.

 

[chickenjohn]

Thanks Dave
It doesn't bother me what the ph is on the ro water but I will try the bottled water to test things.
I use a red sea seawater refractometer and a D-D one to read SG.

 

[chickenjohn]

One thing you can do is get one gallon of distilled water from the grocery store and mix that with the salt and test. That will show you if there is a problem with your source water. It is possible you have a problem with your ro/di unit.

Thanks Dave
Great advice, I did that and it mixed close enough to what it says on the bucket.
Changed all my ro filters and some fresh di resin and mixed with that and readings were exactly what it says on the bucket and ph was 8.2 so happy days again