Review of my plan? New to maintaining my own pool...black algae and CYA way off

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E

epec254

Member
Jun 5, 2022
14
Marin County, CA
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
I’m taking over my pool maintenance from my pool guy. This site / forum has been an awesome resource!!! Love it, thanks so much to the team and community for making this available for free!!!

I’m wondering if folks are willing to comment on my proposed plan and help me with my open questions?

Test results from the TFTestKit:
  • FC: 6.5
  • CC: 0
  • Calcium hardness: 225
  • Total alkalinity: 80
  • CYA: 100
  • PH: 7.7

Current state of the pool:
  • Plaster is approx 25 years or old
    • The plaster is starting to wear off, can see some spots where its completely gone. If you brush, you get bits of plaster
  • Water is clear
  • There are spots of black algae throughout the bottom and stairs

Last year, I completely scrubbed the black algae spots off with a wire brush (took me like 5 hours) and had my pool guy do a shock. The black algae spots were completely gone last year and came back this year.

The plan
Based on the CYA/FC calculator [The Free Chlorine and Cyanuric Acid Relationship] and Ideal chemical levels [What Are My Ideal Pool Levels?]:

  • Calcium harness is low - should be closer to 350-550
  • CYA / FC is way off
  • Alkalinity & PH are OK

My plan:
  • Part 1
    • Fire the pool guy
    • Get a Dolphin M600 that I’ll use for routine cleaning
  • Part 2
    • Partially drain the pool to reduce CYA
    • Retest CYA & FC, shoot for ~40 to 50 CYA and ~3 to 5 FC
  • Part 3 - after CYA & FC fixed

Open questions:
  • Is this the right order? Or should I do Part 2 before Part 1?
  • How much water should I drain? My pool is 15x30 and 3’ to 6’ deep.


THANK YOU!!!
 
Welcome to TFP.

Your plan looks ok. Do Part 2 10 minutes after you do Part1.

How do you chlorinate your pool?

With a history of black algae you need to run your FC hot to keep it from returning. Your FC should be about 20% of CYA (half SLAM level). So CYA of 50 needs a FC of about 9.

@Katodude is our black algae whisperer.
 
At Part 2 you need your FC to be 9 like Allen said.

Also as you are draining get in your pool and clean the black algae with a weak pressure washer. You have to break apart the black algae in order to kill it.
 
Ok thank you! How long do I keep the elevated FC for? Safe to swim while this is happening?

Any sense of how much water I should drain? Its 15x30 ft, about 15k gallons.

Suggestions for a pressure washer that can work under water? All the algae is on the floor so I’ll have to submerge it I think.
 
epec254 said:
Ok thank you! How long do I keep the elevated FC for?
Click to expand...

Until you replaster. Black algae likes to root in the crevices of plaster. With your old plaster I think there are lots of places for it to root.

epec254 said:
Safe to swim while this is happening?
Click to expand...

Yup, it is safe to swim up to SLAM FC level for your CYA.

Basics Archives

www.troublefreepool.com www.troublefreepool.com

epec254 said:
Any sense of how much water I should drain? It’s 15x30 ft, about 15k gallons.
Click to expand...
How do you chlorinate your pool?

For CYA > 90ppm, repeat the test adjusting the procedure as follows:
  1. Fill the mixing bottle to the lower mark (15 ml line) with pool water.
  2. Continue filling the mixing bottle to the upper mark (30 ml line) with tap water.
  3. Shake briefly to mix.
  4. Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark (15 ml line).
  5. Continue the test normally from adding R-0013, but multiply the final result by two.
If you need to dilute the pool water further then apply these ratios:[7]

Pool waterTap or distilled waterMultiply result by
112
123
145
Note that when doing a diluted test not only do you multiply the range of the test you multiply the error rate of the test, so results are a ballpark - not an absolute.
 
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TDS is CYA+CH+SALT.

If you have a large temperature differential between your pool water and fill water then use that.

Or look at the difference in calcium and salt between your pool water and fill water.

Post a complete set of tests for your pool and fill water and @mknauss can help.
 

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Thanks!! @mknauss i just tested the pool water and fill water. I don't have a way to test the SALT - don't think this in the TFtest kit.

Pool water
  • FC: 6.5
  • CC: 0
  • Calcium hardness: 225
  • Total alkalinity: 80
  • CYA: 100
  • PH: 7.7
  • Temp 70.5

Fill water - just tested the CH and CYA
  • CH 75
  • CYA 0
  • Temp 69.8
 
Drain from the deep end. Add water in the shallow end as described in the Draining wiki.
The very close water temperature will lend to some mixing. Over exchange by at least 10%.
 
Thanks! TBH, I don't fully get the instructions

> Put the fill hose in the skimmer, if you have one, in the shallow end. If no skimmer, then use a bucket to put the water hose in and have the top of the bucket above the pool water surface. Be sure to secure the hose to the bucket.

I don't have a skimmer in the shallow end (only deep), so I have to do "If no skimmer, then use a bucket to put the water hose in and have the top of the bucket above the pool water surface. Be sure to secure the hose to the bucket".

I was thinking I would put a 5 gallon bucket on the pool steps, get it approx so the top of the bucket is under the surface and attach the hose to point down in the bucket. But I'm not sure why this is better than just tossing the hose in the pool?
 
You want to limit disturbance when adding water to the pool. The bucket trick keeps that water from mixing too much.
 
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