Lowering Alkalinity Process - White debris at the bottom?

[kmorxi]

Hey guys, I got my K-2006 a week or 2 back and have been learning a ton, my water has no CC and a bit of FC, looks very clear, all the numbers are in a good spot except our water is a bit high in alkalinity. I've been keeping the PH at 7-7.2 and aerating 24/7 which involves pouring about 2 cups of muriatic acid into my 7500 gallon pool a day. I noticed overnight the water became very very clear, an alkalinity test shows it's down from 220ppm to 160ppm, I'm keeping the PH at 7-7.2 and it's working great. Now, I notice a very light coloured slightly off-white 'powder debris' at the bottom of the pool. If it gets kicked up it settles within a few minutes. I'm trying to figure out what's actually happening in the water rather than just following the steps and hoping my water's good. Any idea what that is? My assumption is that the high alkaline water is getting treated with the acid which is destroying whatever alkaline/basic compounds are in the water, and that 'dead' material is sinking. Kinda looks like baking soda. So with this removed, the pool is less alkaline. Does this usually happen when lowering alkalinity? And what's the best way to get rid of it? Just pass it through the filter until it's all picked up with frequent backwashing? Or switch it to waste and vacuum that lower stuff directly out of the pool and just keep topping off the water? I lose an inch or so of water after vacuuming for 15-20 minutes. Not a big deal, but adding in more high alkaline water is a little counterintuitive.

Right now my plan is to vacuum the debris out to waste til there's not much debris left, keep the pool topped up while continuing the lowering alkalinity treatment, and then let the filter clean the remainder while backwashing a bunch. Also, i'm sure an inch of tap water isn't going to be nearly as bad as the stuff I'm vacuuming out.

Any insight is welcome!

 

[Rocket J Squirrel]

It would help if you would post a full set of test results from your K-2006.

FC
CC
pH
TA
CH
CYA
Salt if you use it

 

[kmorxi]

FC 4
Cc 0
PH 7 (keeps drifting up but currently slowly correcting TA)
TA: 150
CH: 220
CYA: 35
No salt, vinyl 7500 gallon above ground sand filter pool. Pic shows how clear it is, very happy, but the chalky debris at the bottom isn't visible. I also vacuumed a lot of it to waste but it'll take a lot to rid all of it

 

[Rocket J Squirrel]

Your numbers look pretty good. I wouldn't get overly concerned about TA. Mine stays at 140 no matter what I do and the pH stays in range and the water is fine.

The TFP Way is not to try to interpolate CYA readings between the lines, but to round up instead. This ensures your FC will not accidentally turn out to be too low. So we consider your CYA to be 40 with an FC range of 3-7ppm. So 4 is OK, but 5-7 would be better.

As to your main question, I don't know what your debris is. I was hoping your numbers would shed a clue, but they don't. At least to me. Sorry.

 

[kmorxi]

Your numbers look pretty good. I wouldn't get overly concerned about TA. Mine stays at 140 no matter what I do and the pH stays in range and the water is fine.

The TFP Way is not to try to interpolate CYA readings between the lines, but to round up instead. This ensures your FC will not accidentally turn out to be too low. So we consider your CYA to be 40 with an FC range of 3-7ppm. So 4 is OK, but 5-7 would be better.

As to your main question, I don't know what your debris is. I was hoping your numbers would shed a clue, but they don't. At least to me. Sorry.

Thanks! It's a new pool and the water was clear for the first week since it was fresh, it took about that week to get the k-2006 test kit, and the cloudiness started just a day before I started lowering the ph in bursts to try and get the TA to drop. I did drop it from 220 to 150 surprisingly so I'll keep at this for a few more days and if it plateaus I'll call that a win where it is! The debris could be pollen or something too, no idea, but I'll just spend 20 minutes vacuuming the ground a day til it's gone!

 

[mgtfp]

My assumption is that the high alkaline water is getting treated with the acid which is destroying whatever alkaline/basic compounds are in the water, and that 'dead' material is sinking. Kinda looks like baking soda. So with this removed, the pool is less alkaline. Does this usually happen when lowering alkalinity?

No, that's not what's happening. The acid just compensates the alkalinity. Eventually, the excess carbonates outgas as carbon dioxide.

There should be no material falling out of solution when adding acid.

When doing the opposite, increasing TA by adding baking soda, with CSI already being high, CSI will locally be extra high until the added baking soda is mixed in, calcium carbonate could form and make the water cloudy.

But I don't see how something would precipitate from adding acid. Unless your plaster is literally crumbling...

 

[MITBeta]

Are you sure the white stuff isn't dead algae? Have you done an Overnight Chlorine Loss Test?

 

[kmorxi]

Are you sure the white stuff isn't dead algae? Have you done an Overnight Chlorine Loss Test?

It could be, the pools under a tree as well so it could be anything from that. I haven't done an overnight test technically but I've been trying to gauge my daily chlorine needs so I essentially test it before bed and sometimes early morning and there's been many times where the FC is 6ish and in the morning it's still like 5 or so with 0 CC or minimal CC. I'll try an actual one but there's definitely.no visible signs of any live algae. I'll do a ton of vacuuming and that test and see where that gets me!