Iron in water source

[BigDave]

@CarlD: I'm pretty sure that dropping the pH is for starting the metal removal process and get and precipitated metals into solution. Next step is holding them in solution with HEDP. Then remove metals with CuLater or using cal-hypo in the skimmer to encourage metals to come out on the filter by creating a high chlorine / high pH zone before he filter.

[CarlD]

@CarlD: I'm pretty sure that dropping the pH is for starting the metal removal process and get and precipitated metals into solution. Next step is holding them in solution with HEDP. Then remove metals with CuLater or using cal-hypo in the skimmer to encourage metals to come out on the filter by creating a high chlorine / high pH zone before he filter.

That's what I thought, but I thought the high FC/pH was to be local to the skimmer, not the whole pool.

[stcohen]

During the process actually backwashed a total of 4 times that produced what looked like rust. Pool was improving then turned dense green. Did not think algae with the high FC and polquat. Did notice a pH drop day after using polyquat-just brought it back up with cal-hypo. Today
pH 7.6
FC 14
Still green, maybe a little less dense. Placed a Culator in trap in case residual Fe.

[CarlD]

Polyquat isn't acidic, as far as I know. It WILL drop FC. However, if FC is very high, it causes a false high pH reading--we warn against this all the time. When Polyquat brought the FC far down, the apparent lowering of pH would simple be a true reading.

[PoolDoc]

I didn't go back and re-read, so I'm not sure what I said.

But normally, you'd want to manage metal removal by STARTING at low pH, with HEDP present, and then gradually allowing pH to move upwards as cal hypo is used.

The goal is to FIRST get the metal dissolved (Vit. C with no chlorine), SECOND to keep it dissolved (low pH + HEDP), and then THIRD to gradually remove it on the filter, while avoiding sudden changes in pH or FC that could re-stain the pool (gradually increasing pH & FC + cal hypo upstream of the filter).