Recurring (and increasing) Black algae spots on Fibreglass pool

I thought that I had been registered for several years but guess I got deleted. The "Getting Started" stickies were rather confusing as the post said I had to register "here" yet the thread was closed????? And apparently I am locked out of putting any pool info in my profile until you "approve" me.

I have an IG Fibreglass pool, 25,000 gal, Chlorine, test with the Taylor DPD-FAS kit, Sand filter, Chlorine feeder, Polaris pool sweep. NO heater. We use well water (tempered with Metal Free), surrounded by oak trees and granite rocks with moss and lichens on them. Maintain FC = 4-5, CC = 0, PH = 7.8, CYA = 40. Phosphate is OK.

Have a 2 level pump, running at low 24/7. Run on high with pool sweep for 6 hours every other day. Brush 2X week.

Last year developed about 30 black algae spots in various areas, which I was able to get off with a chlorine tablet and a brush but they came back. In fall, we drained the pool and did chlorine wash. That worked. Pool was beautiful all winter. Suddenly now the black spots are back with a vengeance, multiplying daily. They do not respond to anything. It is black algae, I can scrape some of it off with my fingernail and it is black/green.

I was recently told that a Chlorine/Aqua Ammonia treatment might work. Supposed to pour 1 gal Chlorine in each of 4 corners of pool and 2 gal of Aqua Ammonia (not sure what % to use-found one on-line of 4%) in center and circulate. And brush. Said it was an old remedy with pool services. Haven't been able to find anything about it on any of the forums. Does anyone know if it works. Is it dangerous? One post said Aqua Ammonia by itself will not kill algae. Sure would like not to have to drain pool again. If I do, what can I use to kill it forever?

Thanx for your help.

Hi grannie, and welcome (back) to the forum!!

Many of the older registrations got deleted over the years with server crashes and changes in the forum setup. Once your registration is complete, you'll have access again to all of the sections of the forum. However, for right now, if you want to search, you can always log out and use the google search feature linked in my sig.

I'll let Pooldoc advise you about this chlorine/ammonia treatment that you're being told about--but I wouldn't try it until he does so. Keep in mind that combining chlorine and ammonia will produce nasty, sometimes fatal gasses. Once they're both in the water that shouldn't be an issue, but just be careful when dealing with this combination. I'm not sure that you can actually kill black algae forever, once you get it--but again, Pooldoc is the one that needs to discuss this with you. I'll alert him to this thread and see if he can help.

Sorry your post and membership got lost in the crush -- not sure if you still need help, but your membership has been upgraded. -ben

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,

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!