And the Black Algae is back... Need a "stonger advice"..

[HardTrance9]

Hello again!

Pool test:

FC 7
CC 0.5
pH 7.5
TA 110
CH 130
CYA 100
Temp 29º Celsius (84°F)
salt 3,300 (Quantab salt strip)

Over the last couple of years this pool is the only one I have been having problems with. It has black algae and seems to never go

First time, after some discussions, here you all helped me with this pool a couple of years ago. Summary: apply a ultra high mega shock level (higher than what the pool calculator would suggest),
make to checks per day on the FC and pH, etc., brush, brush and brush and vacuum, etc., for around 6-7 days.

This worked very good and it lasted probably 8 months until "blackie" decided it was time to revive...

After that, as that was an "expensive and time consuming" solution (2 checks per day, etc)., we tried some products (I will name those later on here) and they worked but for shorter times..

Bottom line: what do you suggest it can be done so this black algae problem can be removed for ever?

Pictures show now the black algae coming back. On the steps, you can barely see it on the left (sorry for the picture take) and in the other one, just below the return... black spots coming back...

Do we have to remove the current finish? and then apply a new finish? We are kind of desperate for a solution that will work... Of course the only one not applicable is to RE-DO the whole pool, but other options could work.

Any help and suggestions will be much appreciated.

Thanks everyone!

 

[AimeeH]

Well the first question is how was CYA tested?

If it is really 100 your FC is on the low side which is probably why there is algae. Depending on how you got a result of 100, it could be actually a lot higher in which case FC needs to be a lot higher.

 

[Casey]

I suspect your use of pucks is driving your CYA on the high side. You really need to keep that in check. A pool with such a high CYA as 100 needs a target FC of 12ppm FC. You are now at the minimum of 7ppm FC. That's is you know the CYA is a solid 100ppm. If it's over, you're really low on FC and it is inviting black algae to grow. I don't think you need *stronger advice*. I think you need to watch your numbers a lot better when it comes to high CYA or use the proper amount of FC if you're going to play with a higher than normal CYA level.

If you want a solution that will work, reduce the CYA level and run a higher than normal FC level and brush the pool daily and the Black Algae will go away.

Good luck.

 

[chem geek]

The circulation might be poor in the areas where the algae shows up. You can also try pointing the returns more downward, though that will reduce skimming action. Is this a saltwater chlorine generator pool (since the salt is so high)? I agree that it does sound like the CYA got too high through use of Trichlor tabs and I suspect the FC wasn't kept up along with it, at least not consistently. Black algae usually takes lower FC/CYA ratios for an extended period of time to develop. It's slow growing, but once established it is chlorine resistant due to excretion of a waxy layer.

 

[BoDarville]

You have been given good advice by some of our finest.

We recently added an article dealing with black algae that you may want to take a peek at: http://www.troublefreepool.com/content/180-Black-Algae