Runoff EC consistently LOWER than input EC?

[FrankCos]

I have been growing several plants in coco coir, 3-gallon fabric pots, Fox Farms hydro nutes, and fertigating twice a day with enough volume to get substantial runoff. The first three plants (now in late flower) have always given runoff EC slightly to moderately higher than the input - so the input is, say EC 1200 us/cm, and the runoff is usually 1400 - 1600.

There is a fourth plant (Critical auto), which I started growing about a month later, and is now at day 64, and about 3 weeks into flowering. She started out giving runoff about 100 - 200 points higher than the input EC, as expected. Then, at day 51 (day 10 of flowering) she started giving runoff that was about 200-300 points LESS than the input. So today, for example, I fertigated with EC 1050, and the runoff was EC 770.

Any idea what would cause this? The plant looks reasonably heathy. She is quite small, because I grew her for the first 6 weeks under a weak seedling lamp, and only after that (when I got a second tent and LED grow light) did she get the correct amount of light.

[Low]

When it’s less decrease run off or frequency of feed. If you don’t want to do that increase feed strength.

Having higher run off means your nutrients are too strong or you’re not feeding enough in volume to push out salts. Find balance. Equal in equal out.

The run off will fluctuate depending on the time of day you water. Morning noon night all will reflect different PPMs in run off based on plants consumption.