Brown dusty residue on bottom of pool.

[Rubenjam]

All my chemicals are excellent, water is clear and sparkling. I used a water clarifier and since then I have a brown dusty residue on the bottom of the pool that vacuums up but returns with hours. If I leave the cartridge filter off it remain clear of the residue but once the filter starts the problem returns to the pool base. What could it be and what is the solution? I have noted on the site that other pool owners have the same problem without a fix.

[waterbear]

2 hours ago, Rubenjam said:

All my chemicals are excellent, water is clear and sparkling

This tells us nothing. Please post a full set of test results. I have some suspicions but need to know your actual water parameters. Also, is this an inground or above ground pool and is it plaster, fiberglass, or vinyl? Are you using chlorine or a different sanitizer? If you are using chlorine what is your chlorine source (trichlor, diclor, cal hypo, or liqiud chlorine/bleach)? Do you use well water or city water to fill the pool?

2 hours ago, Rubenjam said:

have noted on the site that other pool owners have the same problem without a fix.

Please provide a link to the thread(s) where others have had the same problem so I can take a look.

[Rubenjam]

Thanks Waterbear for you your interest. The link for the problem others have had was "Help Vaccuming Out Residule in Pool" with that spelling. Above ground vinyl pool 12000 litres. Using Chlorine Hy-Clor Liquid chlorine. City water. Free chlorine 2.48, Total chlorine 2.48, PH 7.6,  Cyanuric acid 64, Total alkalinity 110, Total alkalinity Adjusted 89, Total Hardness 102, Magnesium hardness 0, Calcium hardness 102, Phosphates 0, Total copper 0.2, LSI-0.51.

 

[waterbear]

9 hours ago, Rubenjam said:

The link for the problem others have had was "Help Vaccuming Out Residule in Pool" with that spelling.

Please provide the URL for the thread in question. Search on Help Vaccuming Out Residule in Pool produced over 1000 results.

9 hours ago, Rubenjam said:

Free chlorine 2.48, Total chlorine 2.48

9 hours ago, Rubenjam said:

Cyanuric acid 64

 

This jumped out. Your FC is WAY TOO LOW for your CYA level. With a cyanuric acid of 60 to 90 ppm your need to maintain your FC in the 5 to 10 ppm range and shock to 20 ppm (don't go any higher with a vinyl pool).

My suspicion, based on your FC and CYA,  is that you have a mustard algae outbreak since it reappears after vacuuming it. Mustard Algae can appear as brown. Filters will not filter out suspended algae and I suspect it was their before you used the clarifer, making the water cloudy, which is why you probably used the clarifer in the first place. Am I correct? Clarifers will cause suspended particles to clump together.

Mustard algae requires VERY HIGH FC to kill and this is not possible in a vinyl pool. Second best option is to get a 60% polyquat algaecide (poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride] ). Iwould not recommend a quaternium or copper based algaecide, you want 60% polyquat.

The cure is to lower your CYA to 30 ppm and not let it go above 50 ppm. The only way to lower CYA is to replace water, in your case around 50%. This is best done by a series of partial water changers since lowering more than a foot at a time in a vinyl pool could cause problems with the liner. Also, once the CYA is in range DO NOT USE ANY stabilized chlorine (trichor or dichlor) since they will continue to add CYA. Trichlor will add 6 ppm CYA for every 10 ppm FC added and dichlor will add 9 ppm CYA for every 10 ppm FC added. Use only liquid chlorine (sodium hypochlorite) or Cal Hypo but be aware that cal hypo will add 7 ppm calcium harndess for every 10 ppm FC added.

 

Saturation Index is not a measurement to worry about in a vinyl pool. It is for a plaster pool to determine if the water is aggressive and will etch the plaster or will cause scale to deposit on the plaster. Calcium hardness is not that important in a vinyl pool either. Just keep it above 100 to help prevent foaming (soft water has a tendency to foam).

Since you are using an unstabilized chlorine source (Liquid Chlorine) you want to keep your Total Alkalinity between 80 to 100 ppm. Both trichlor and dichlor require a higher TA (100 to 150 ppm) since they are net acidic (acid on application and acidic on sanitation/oxidation) and will cause TA to drop (along with pH) while unstabilized chlorine sources are net pH neutral (alkaline on application and acidic on sanitation/oxidation) so pH rise from outgassing of CO2 is more of an issue and the higher the TA the more carbonation in the water and therefore the faster the pH rise from outgassing of CO2. Hope this helps.

This pinned posts might be helpful:

https://www.poolspaforum.com/forum/index.php?/topic/52523-some-truths-about-ph-and-ta/

[Rubenjam]

Thanks Waterbear your a legend, I will add a couple of photos to confirm your diagnoses. 

[waterbear]

The thread you are linking too describs mustard algae and confirmed that the CYA was high. Your photo looks like mustard algae but it is hard to say. Could also be pollen but it ususally floats on the surface and does vacuum out. A useful rule of thumb is that if it doesn't vacuum out and passes through the filter there is a good chance it's algae. My question is how did your CYA get so high?