50/50 Coir/Peat Moss runoff question

I am growing in a 50/50 Coir/Peat Moss mix with a touch of perlite for good measure. Fox Farm nutes ph'd at 5.8 (after the nutes were added) but my runoff is measuring 5.1 on one plant and 5.5 on the other (it was a water to almost 30% waste versus volume).

Should I be concerned? Is it also advisable to flush each month when using this medium?

UPDATE: Third plant ph runoff at 4.6 and wouldn't budge! Water in was PH of 6.0 and I used 2 gallons of water on a 3 gallon pot.

Is ph runoff even significant in a soilless medium?

Yes, it's very significant. It says that your medium pH is low enough to pull down your soup from 6.0 to 4.6. I would say dangerously low.

Now what is causing that? I've never used coir or peat, but I have heard that peat will have a higher pH, but it's been awhile. It could be some nasty fungus growing in there. Best to flush with a H2O2 solution and see what happens.

HTH