Swg Chemical/corroding Problems

[chem geek]

Put your full set of accurately tested water chemistry parameters into The Pool Calculator and see what you get for the saturation index. If you increased CH and then used pH Up to adjust pH which would have also increased TA, then your water may be over-saturated with calcium carbonate and that the white stuff is undissolved calcium carbonate.

[rocket]

Put your full set of accurately tested water chemistry parameters into The Pool Calculator and see what you get for the saturation index. If you increased CH and then used pH Up to adjust pH which would have also increased TA, then your water may be over-saturated with calcium carbonate and that the white stuff is undissolved calcium carbonate.

That's probably what happened. In fact, I added them at the same time. The water got cloudy for a couple days and I noticed the powdery stuff lingering on the bottom. I tried to sweep it up but no luck. My CH level is now 245 I believe. How do I get rid of the powdery stuff?

[chem geek]

The answer depends on your saturation index. If the index is too high, then you need to lower the pH, TA and/or CH. 245 ppm for CH isn't high, however, so the saturation index would only be high if your pH and/or TA were very high. Lowering the CH can only be done (easily) through dilution, though in extreme cases there are metal sequestrants that focus on calcium, but I wouldn't recommend that. TA can be lowered through the procedure described in this post. pH can be lowered with acid, but you don't want your pH to be too low and it will be hard to maintain it much below 7.5 in an SWG pool anyway.

My hunch is that you just locally over-saturated the water with your "too quick" chemical additions. When I've added pH Up in the past, I've gotten some calcium carbonate pieces form, but they eventually dissolved with some brushing. First, be patient and brush. If yours don't dissolve, then you can vacuum them up. If you temporarily lower the pH somewhat, they will probably dissolve more quickly.

I'm assuming that this powdery stuff is in fact calcium carbonate. If instead it's some sort of filler, then that may only be removed through vacuuming or filtration (assuming you can get this stuff to the floor drain or skimmer.

[rocket]

Does the drain have metal screws? The pool guy said he would replace all screws and could do so without removing the water. Seems the drains would be hard to do 8.5 feet under water.

[rocket]

Chem you have said "FC to be a minimum of around 5% of the CYA level" Is this in order to protect from Algae or corrosion? I thought one of the main reasons of corrosion was due to lack of CYA in relation the FC. Or is it just lack of CYA period, in other words if you have 60 ppm of CYA it does not matter how much FC you have in regards to the corrosion issue.

[chem geek]

Chem you have said "FC to be a minimum of around 5% of the CYA level" Is this in order to protect from Algae or corrosion? I thought one of the main reasons of corrosion was due to lack of CYA in relation the FC. Or is it just lack of CYA period, in other words if you have 60 ppm of CYA it does not matter how much FC you have in regards to the corrosion issue.

The minimum FC as a % of CYA is to prevent algae growth. As for corrosion, pH is the biggest factor, but the amount of active oxidizer is also important and that is roughly proportional to the FC/CYA ratio when CYA is present and is roughly proportional to FC when CYA is not present. So the lack of CYA with "normal" amounts of FC (i.e. 1 ppm or higher) is about 10 times or more higher in active oxidizer (i.e. hypochlorous acid) concentration than water with an FC/CYA ratio of around 0.1. The corrosion rates will be much higher, though in practice this is mostly seen in pools with no CYA and higher salt levels -- i.e. an indoor pool with no CYA and an SWG at 3-5 ppm corroded one user's stainless steel in less than a year.