nice one guys defo going to flush 2mo i have some canna flush to so should help keep all the good bacteria left in so should i just flush with a ph adjusted water like 6.5 until run off becomes clear then check ph and ppm again?
I don't think you need a flush agent. Just 50-100% runoff (compared to container size). Just a pure-water feed followed by half-strength nutes would probably turn it around quickly too.
You don't need to ph the flush water because it won't have enough buffering capability to hold that ph. I.e., it's a waste of time. Whatever you ph the water to, it will quickly give way to the ph of the soil (the salts, the materials in the soil which interact with water). Since your soil is acidic, if you were going to ph your water, ph it to 7.5 to help pull the soil higher. But, like I said, if it's low-ppm (pure water) it's going to have an insignificant effect on the ph of the soil, which will have a far stronger effect on the water's ph.
It's good you caught the acidity when you did. When my runoff went below 5.4, that's when I started having serious problems. Keep in mind that the soil ph rises as it dries. So, just because you see 5.4 when it's wet doesn't mean nutrients are locked out. If you let the soil dry adequately it will go up to 6.4. (After you get the salt problem fixed, and runoff is more like 5.8-6.0, the soil will go as high as 6.8-7.0 as it dries.).
If you're really into dialing in your soil ph, get a Control Wizard Accurate 8 ph probe. They cost $60. It's more accurate than those cheap probes sold at Home Depot. It's not completely accurate, but like monitoring runoff, you see trends as you take readings at different levels of dryness, different locations in the soil, etc. It's handy info in *addition* to runoff ph. Both runoff and probe measurements are a waste of time if you have your soil/nutes dialed in. But, the two together are useful when dealing with unknowns.