Recurring (and increasing) Black algae spots on Fibreglass pool

[grannie14]

Thanx,PoolDoc,

Yes, I really still need help. I've been trying to scrub and scrape the spots I can reach and not much success. And now our pool is polka dotted! Have you heard of this Aqua ammonia with Chlorine remedy? Seems if the two products are poured in separately into the water, there is not much chance of them mixing before diluted. What I really need to know is if this is a good remedy and what % of aqua ammonia to get.

Thanx,

[PoolDoc]

Aqua ammonia + chlorine is the functionally the same as Yellow Treat.

IF you do it correctly, and IF don't mind taking your pool out of service for 2 weeks, it will probably greatly reduce the black algae.

There are other options, that do NOT require that you stop using your pool:
1. High levels of borates will probably help . . . but slowly. (Add lots of borax + some muriatic acid)
2. Establishing VERY low phosphates will help, but we'll need to inventory your chemical regimen VERY carefully, since many pool chemicals ADD phosphates!
3. Persistent brushing + use of polyquat will help.
4. Sustained high levels of chlorine (10 - 20 ppm) will help

You can combine #1, #2, and #3 OR #1, #2, & #4 (Polyquat isn't really compatible with very high chlorine levels). But you need to realize that, once black algae is established, dealing with it is more a matter of control, than cure. It tends to penetrate imperfections in your pool's surface, and remnants of live algae will remain there, out of reach of any chemicals.

To pursue any of these successfully, you need to follow a careful plan and accurate consistent dosing. I can help, but it will make it easier if you will fill out the pool chart:

Pool Chart Entry Form
Pool Chart Results

Good luck!