Haze
What you are describing is not all that uncommon.
I experienced the exact same thing when I first got my RO/DI unit up and running.
I discussed my resulting low pH of the newly mixed saltwater with a technican at Instant Ocean in Mentor Ohio.
Here's what I learned;
As municipal tapwater enters into the RO/DI unit, it has a certain level of carbonates, bicarbonates, calcium, magnesium and other stuff in it ..... AND CO2 gas, all of which are dissolved in the tapwater.
As this water passses through the multiple stages of the RO/DI, much ( most ) of the carbonates, bicarbonates, calcium, magnesium and other stuff is rejected by the RO membrane.
In other words - these compounds are not "pushed" through the membrane. Some of this stuff get's through - but most is removed by the RO process/membrane.
The CO2 gas on the other hand - much of it moves right on through this membrane. CO2 gas is not a solid .. it's a dissolved gas. The gas molecule is very tiny relative to the other dissolved solids. This RO water still contains much of the original CO2 gas that was in the pretreated tapwater.
It's still in there - we just can't see it.
As this water then passes through the DI - again much of the CO2 gas is not removed.
The result is RO/DI water that can contain a lot of CO2 gas.
So now we have RO/DI water - that has close to neutral pH, very little ions left in it ... but may still contain CO2 gas in solution.
Often the pH of this water can actually be somewhat acidic - dropping down below 7.0 ( if measured with a freshwater pH test kit ). I've tested my freshly made RO/DI water in the 6.8 range before.
As we mix the saltmix with this "FRESHLY MADE" RO/DI water ... we may end up with a batch of saltwater that has a low pH.
Down in the mid to high 7's ....... as opposed to the 8.2/8.3 pH range we'd like to see.
So what do we do about this.
AERATE THE RO/DI WATER BEFORE MIXING IN THE INSTANT OCEAN SALTMIX
Don't use an airstone though - just run the RO/DI water into your plastic holding/mixing container ... and place a heater and strong powerhead in the RO/DI water.
Place the powerhead on the bottom of the RO/DI water container ... pointing up .. so it moves water from the bottom of the container up to the top.
If the surface is sort of bubbling and rippling .. you got it right.
Let this RO/DI water sit overnight like this - and much of the excess CO2 gas will escape the RO/DI water.
The level of CO2 gas will reach an equalibrium with the level in the room. This is a good as you can expect.
Then ....... proceed with mixing in your saltmix.
Then ...... let this new batch of mixed saltwater aerate again using the same powerhead/heater/procedure.
If you try this ... I'll bet you'll find that the newly mixed batch of saltwater will have a higher pH.
Mine went from pH of mid/high 7's before I followed this aerating procedure..... to around 8.2 pH after following it.
Excess CO2 gas that is in the water can and will pull the pH down.
Try it next time and see what happens.
If this does not cure the low pH of your mixed batch - please let us know.
You should not need to add marine buffers to newly mixed batches of Instant Ocean synthetic sea salt.
If you do need to tweek - it's always better to tweek the tankwater - not the new mixed saltwater batch.
Good luck.
