I'm confident that when I pump into my RDWC, the mix is fully dissolved. Just from my own experience, I'm not a fan of using a pump on the initial mixing. I found it took too long, and just wasn't quite enough to get mixed well without leaving it for a couple days.
I do swear by the drill paddle though. It was cheap, and it makes things so easy. When I'm mixing in a bucket, which is most of the time, I use my cordless drill. When I mix the concentrate into the barrel, I use a corded drill that has a little more power. It gets that barrel mixing up really well though. I give that a few minutes, then hook up my transfer pump. I have a garden hose connected to one side of a coupler. Then I have a pipe coming out of the pump, that comes up to about the 3/4 level of the barrel. I turn the pump on and let it circulate an hour or two. Then I hook up the coupler, and pump out.
At 6g/gal you're fine there. Are you adding calmag, or anything else?
Have you checked your scale for accuracy? With only 15g, if you're off by just a tick, it can have big consequences. If I'm off by 5g when weighing out 325g, not as big of a deal (6.6g/gal instead of 6.5), but on 15g if you're off a few g for 2.5 gal, that could raise it too.
It could be that your meter needs calibrated.
There are a lot of things that could influence that number, even to the point where it isn't accurate.
It could be as simple as it's time to change the filter in your RO.
The real thing is how do the plants look? Are the leaves light green, dark green, or that really nice grass green? That's the important thing. As long as the leaves are good, don't sweat ppm/ec/blah blah blah. It can really be overkill for MC.
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