Black algae and high pH

[lkcrook]

Hi everyone! First post here. We bought a house with an older plaster pool (possibly late 90s) in FL a few months ago. (This isn’t our first pool, but it’s been 5 years and had different issues, plus was in OK). This pool had a sand filter and old equipment, but we had a company come out and they replaced it with a Jandy cartridge filter, SWG, new pump, new heater, etc. about a month ago. A few days before they replaced all this my husband accidentally drained the pool (I was still living in a different state and he was too busy to deal with pool, it turned green, he backwashed and must’ve left something open, oops!). So, it was filled with well water just prior to the new equipment. The pool has been clear and pH and chlorine were ok according to pool store as I waited for my TFT test kit. However, we were so busy with new jobs, renovating our whole 1st level (demo kitchen, master bath, etc) and then Covid hit our house, that the pool has been neglected. It’s still clear but here are some problems I’d like your help with:

1. water chemistry is off
pH 8.2
FC 4 (chlorine on the daily test with R-0600 was bright yellow, maybe over 5?)
CC 0.5
Ca 200
TA 170
CYA 30
NaCl 3500
I’m going to add some muriatic acid to lower pH, but wasn’t going to adjust CYA until taking care of next issue. Sound ok?

2. One thing I didn’t think was that big of a deal was a few dark spots on the grout lines, which now I believe is black algae. We have landscaping near the pool so I’m sure that doesn’t help. The spots above the water scrape off easily and are greenish on white paper. But I’m noticing black spots that I thought were sand (more on that later) but don’t scrape off with pool brush. We have a lighter colored surface with darker specks so it was hard to notice at first until it started getting bigger. When I finally got in the pool with goggles it looks like a black stain on the surface of the pool, but won’t scrape with my nail. Think that is black algae? It‘s more prevalent by the lights, guess I need to take those out? Do I just clean those or need replacing? I just bought a small brush & am going to work on it tomorrow. Will it go away with the SLAM method? We are off this week & want to swim, will that be ok with SLAM?

3. We keep having lots of white sand in the pool, possibly from the old filter? Some is coarser than others. We have a Dolphin cleaner that keeps ending up with sand in it and we see it on the bottom of the filter container when we clean the filter. We can’t figure out how so much sand is still in the pool after a month. We don’t have sand on our feet or anything, there’s a lanai around pool area and not much exposed ground outside the pool. Plus the outside sandy dirt is black. Any idea how to get rid of it all?

Any suggestions are greatly appreciated! We don’t have a ton of time during a typical work week right now and I thought about getting a pool company to take care of it for now, but not sure how great of job they’d do. Even though I’m off this week I’m still getting over Covid & trying to order stuff for the house Reno but I’d like to get the pool sorted out.

thanks!

 

[jedigrover]

Generally with black algae, if you pick at it with a bamboo skewer or rub it with a trichlor puck, it will start to scratch off. You don't need to SLAM for black algae. You do need to operate chlorine at a high level (high normal, or even a little higher). The key is to brush with an algae brush (wire brush) often--as often as you can. Black algae makes a waxy/slimy cap that protects it from the chlorine. You have to scratch through that enough that chlorine can get to it.

Rubbing individual spots with a trichlor puck can really help.

Some people use a garden pump-up sprayer with liquid chlorine (10 or 12%) an spray the spots. But you must brush, brush, brush!

Definitely pull the light from the niche and clean it.

I would also pull the eyeballs and clean every part of the wall fittings. And if you have a pool sweep, take it apart and clean every bit.

For the white sand, is it sand, or is it calcium scale? That often appears as a white, gritty material. The reason I ask is that the high TA and pH you have puts your CSI strongly on the scaling side. So my bet is that it is calcium scale.

 

[Texas Splash]

Welcome to TFP! Please review the link below, update your signature with all of your pool and equipment info, and let us know if you have any questions. Also see Pool Care Basics.

Black Algae

This guide provides a step by step procedure for eliminating black algae in your concrete or gunite pool. Read full post here.

www.troublefreepool.com

 

[Bperry]

In addition to above, sometimes what looks like black algae is just dark green algae and it’ll lighten up and go away with a SLAM and even just elevated levels of chlorine. I had some and was able to get rid of it after about a week of elevated SLAM chlorine levels but only brushed once or twice. I’d personally avoid the wire brush and try a nylon brush first since it’s less damaging to the plaster. You might get lucky.

 

[lkcrook]

I got the pH down to 7.8, but it went back up over 8 in a couple days. We usually keep our fountains on, so I turned those off. I don’t know how to stop our spa spillover without putting it in spa mode though. The cover at the bottom of our spa is broken, how do I find out a replacement model? I can’t find one that’s the right size that is mostly solid like this one.

I spent several hours scrubbing the algae off the grout, but it’s still a little stained. Is there a cleaner I can use? I tried bleach. The algae on the sides/bottom of the pool is very stubborn and will barely budge even with a wire brush. What can I use on that?

the sediment definitely looks like sand. I emptied our cleaner before running it & it had a bunch of sand in it again. I’m going to include some pictures.

 

[Texas Splash]

The stains are going to take a while. They, and the plaster/grout, look old. Consistent chlorine and brushing over time. Sand? You have a cartridge correct? Are you close to the beach or where wind could blow sand into your enclosure?

For the pH, your last PoolMath log shows a TA of 140. You need to lower that. You do that by lowering the pH with muriatic acid. When the pH hits 8.0, use enough acid to lower the pH to 7.2. Each time you do that it will lower the TA a little. Keep doing that until the TA gets down to around 60 or so. That should help.

 

[lkcrook]

We’re not sure when the pool was built, but the house is from 90s so it’s probably about that old. But it’s still a pool! We’re not ready to resurface the pool anytime soon. The sand is a mystery to us, still thinking it’s from the old sand filter that we replaced a month ago. Could it be the plaster deteriorating? The pool company that replaced our equipment said it looked ok, but I don’t really trust them because of some other things that came up.

I put more muriatic acid in the pool today. Is there any other way to lower TA?

 

[gingrbredman]

Wow, you got busy real fast and had a lot thrown at you!

but wasn’t going to adjust CYA until taking care of next issue. Sound ok?

When you start the SLAM, it will be much more managable with CYA at 30. When you are done and all things clear, you'd want to be closer to 60 in Florida. But 30 will keep the SLAM chlorine levels a little easier to deal with.

want to swim, will that be ok with SLAM?

TFP says swimming is safe at SLAM levels

I thought about getting a pool company to take care of it for now, but not sure how great of job they’d do.

No one is going to take care of your pool like you do. Even with a busy life, a little time during the week to manage the chemistry is very easy. A service is likely going to just dump chlorine, or use tabs, and care little about the overall balance, which is seems you are very keen on getting right.

Is there any other way to lower TA?

The best way is to lower PH to around 7 with muriatic acid, then aerate to raise. You have the tools for aeration, so thats good, Then repeat. It is annoying, I know, but the best way to get it lower. I have tried the process several times and my TA likes to settle in around 100 once the PH stabilizes. TA is the last measurement I look at if it is "close" to the range, and all other tests seem stable.

Before you SLAM, it would be best to get the PH and TA a little more in control. Once you get to SLAM levels, and chlorine is above 10, the PH test can get skewed, so you want to have it under control because you wont be looking a that during the SLAM.

The sand is a mystery. The "old sand" shouldnt be present in the system after the change to cartridge, but it may be worth opening up the filter and taking a peak inside as well.

 

[jedigrover]

The sand is curious. I get some sand in my pool from my old sandstone coping eroding, but it looks like you have brick.
On the black algae, you just have to keep the chlorine up and brush often. Don't really try to scratch it all out with the wire brush in one go. It won't work & you'll do more damage to the plaster. You just want to break through the slime/wax cap on them so the chlorine can do its work. It will take quite a while and test your patience. After you think it's gone, keep the chlorine levels at the high end of your normal range and keep an eye on it.

I personally believe that on old plaster like this, it gets roots so far in that you are never truly rid of it. I have very old plaster that is damaged (hopefully can get my pool resurfaced within the next year) and I have to battle it every year at early spring when conditions change quickly. Even after cleaning every visible and many invisible spots, and even holding a FC of 7 consistently, I will find a spot or two trying to develop throughout the summer and just have to keep on top of them with a brush and raise my residual up to 10 for a week.