Mustard Algae or not Slammed twice

[JDB]

I have had problems with something on bottom that was like fine powder or dirt/silt. Kept vacuuming out only to return, I recently changed sand (checked laterals) & about week later still getting so decided to SLAM.
Week 1 Slammed Monday evening through Friday Morning, CYA 45 so FC @ 18 checked 2-3 x's day Vacummed & brushed as needed to remove, Improved look on bottom all week & finally on Friday No Chlorine drop over night & "0" CC.
Seen just a speck or 2 on bottom Friday afternoon, Leaving for weekend & chlorine level was still about 12ppm so vacuumed & added 1 gal. liquid chlorine before we left in late afternoon.
Came back home on Sunday & had dirt in middle & a few more spots @ end away from return/skimmer with a FC level of around 8ppm & CC of 1 so vacummed out again & started a slam on Monday since not enough chlorine on hand, CYA 35-40 so put FC @, Tuesday morning right at sunrise checked again & no Chlorine drop & CC "0" now today Wednesday morning 1 or 2 little spots on same side of return about 20 ft away so added about 1/2 gal shock from spots back to return to try to get on top of the spots to see if more direct contact may help them.
Should I use something like a Pool life algaecide 90 to help with keeping away???
Last week I used 15 gallons of liquid chlorine & this week used like 2.5 gallons to slam plus a little extra during day yesterday & today just to keep higher for a bit since no one was swimming.
Don't want it to come back like has before also what about ionizers or ultra violet light, my above ground is in sun ALL DAY with no trees around it.

 

[domct203]

I have had problems with something on bottom that was like fine powder or dirt/silt. Kept vacuuming out only to return, I recently changed sand (checked laterals) & about week later still getting so decided to SLAM.
Week 1 Slammed Monday evening through Friday Morning, CYA 45 so FC @ 18 checked 2-3 x's day Vacummed & brushed as needed to remove, Improved look on bottom all week & finally on Friday No Chlorine drop over night & "0" CC.
Seen just a speck or 2 on bottom Friday afternoon, Leaving for weekend & chlorine level was still about 12ppm so vacuumed & added 1 gal. liquid chlorine before we left in late afternoon.
Came back home on Sunday & had dirt in middle & a few more spots @ end away from return/skimmer with a FC level of around 8ppm & CC of 1 so vacummed out again & started a slam on Monday since not enough chlorine on hand, CYA 35-40 so put FC @, Tuesday morning right at sunrise checked again & no Chlorine drop & CC "0" now today Wednesday morning 1 or 2 little spots on same side of return about 20 ft away so added about 1/2 gal shock from spots back to return to try to get on top of the spots to see if more direct contact may help them.
Should I use something like a Pool life algaecide 90 to help with keeping away???
Last week I used 15 gallons of liquid chlorine & this week used like 2.5 gallons to slam plus a little extra during day yesterday & today just to keep higher for a bit since no one was swimming.
Don't want it to come back like has before also what about ionizers or ultra violet light, my above ground is in sun ALL DAY with no trees around it.

My guess is that you ended the SLAM too early with 'specks' of algae on the floor.

If you suspect mustard algae, you can raise the FC to mustard shock levels after you pass all 3 criteria to end a SLAM (pass OCLT, CC=<0.5ppm, water clear of algae dead or alive) and hold it at mustard shock level for 24 hours.

If the pool is in the sun all day it is already getting plenty of UV exposure.

Are you 100% certain on your CYA level? If you are getting between 40 & 50ppm as a CYA result, round up to 50ppm and SLAM at FC 20ppm. Are you testing CYA outdoors on a bright sunny day, back to the sun, reading the test vial at about waist level in your shadow?

More on mustard algae here:
https://www.troublefreepool.com/content/148-mustard-algae

 

[PAGirl]

Are you brushing regularly?

 

[JDB]

There where no specks of anything on floor when i stopped slam, I vacuumed twice a day once in morning and a hr or two before sunset to add more chlorine as sun was setting, no longer on pool behind trees checked chlorine level 30 min or so after dark then within 15 min of sun starting to rise. First few days added quite a bit last few days able to start less & less chlorine started on a Monday night ended on Friday Morning with no OCLT same as night before & "0" CC that morning.
Then later towards Late afternoon I seen just a couple brown spots again like I had before but more of, so I was leaving for weekend so put a Gallon 1/2 in to raise up again, got back Sunday evening was appox. 4-5 spots, vacuumed before grand kids swam then started slam on Monday Afternoon again, checked Monday night added to bring to 18 with a cya of 40 (tested inside at waste level) next morning again passed OCLT "0" CC clear water (always clear), didn't see anything but possible dirt last couple days just got in pool so brushed thouroughly going to rain possible checked pool

FC 7
CC 0
ph 7.6
ALK 90
CYA 40
Going to put another gallon of shock in tonight just due to heavy rain here shortly & air temp drop of about 12 deg. so no swimming for a bit
just wanted sure if a algaecide may help keep from reaccuring this yr since have had this problem for more than 1 season.