algae problem possible pump is too powerful?

[Regmcm]

good day all. first sorry for the long post but i wanted to give some context in case we have missed something obvious?

We inherited a in ground pool when we bought our house 3 years ago. It was in disrepair as it hadn't been used in over 15 years. here are the specs
9m x 4 m.
36 cubic meters
Sand filter (no idea of specs as the labels have washed off however it takes about 40 kg of sand to fill to 3/4 and it's about 800mm tall and 500mm wide)
Pump specs. recommended for pool size of Pool volume: 25-50 m3
Electric power: 800W, 3.2A
Maximum flow rate: 15 m3/h
Maximum pressure: 15m

I don't have a fancy water test kit as they are impossible to find here in Bulgaria so i've been using the red / yellow liquid test kit which measures Chlorine and PH level
we have a few neighbours here with similar pools and this is what they use with no issues. I check the chlorine / ph levels weekly and add granular chlorine or Minus ph as required

We keep the Free chlorine at between 3 and 5 ( i assume that's PPM?)
and PH 7.5

When we bought the house the pump had been stolen and the pump house and electrics were underground and were in a shocking state so we replaced everything and moved pump and filter above ground.
We removed the sand in the filter washed and put back.

All was good with pool between june and July crystal clear water and chem levels constant, the only thing we noticed that was after a heavy rainfall the PH level would rise so we added minus ph to bring it down.
Then mid August air temp rises to above 35 and close to 40. Water temp reached 35 at one point and at the same time green powder started to form on bottom of pool. we looked online for help and followed instructions
(half emptied pool, shocked with chlorine etc) but nothing worked. vacuumed pool every day and backwashed filter daily but pool would just go cloudy and green powder returned next day. We didn't have a summer cover in place
and it gets quite windy, we are also close to the coast so we assumed it was fine sand getting into pool and decided to empty pool for the summer with clean water and start again following year with a pool cover in place.

So this year we started from scratch, jet washed the pool and re filled, bought a summer cover to keep debris out when not in use . All good until exactly the same time in August!
Green powder forming bottom of pool, went through the same process RE shocking but to no avail. After a process of elimination i decided it must be a sand filter issue so i emptied the
Sand and lo and behold it was bright green and disgusting, So We replaced the sand in the filter with one recommended by a pool supplier its 0.25 mm = 0.5mm (granular size)

Ran the pump and lo and behold the pool cleared up in 24 hours! christal clean again and the wife was happy. Alas this lasted about 3 weeks and now its gone back to green algae yet again.
We are at our wits end. So now after some research i think maybe the sand in the filter has become "channeled" due to the pump being too powerful?

We have decided to close the pool for the winter, but we are not going to empty. And next year change the sand in the filter to the more expensive silicon
type which allegedly does not have issues with channeling? or should we get a smaller pump? (the pump is one speed and cannot be regulated).

Any comments or advice would be appreciated.

Many thanks Reggie

 

[Bperry]

good day all. first sorry for the long post but i wanted to give some context in case we have missed something obvious?

We inherited a in ground pool when we bought our house 3 years ago. It was in disrepair as it hadn't been used in over 15 years. here are the specs
9m x 4 m.
36 cubic meters
Sand filter (no idea of specs as the labels have washed off however it takes about 40 kg of sand to fill to 3/4 and it's about 800mm tall and 500mm wide)
Pump specs. recommended for pool size of Pool volume: 25-50 m3
Electric power: 800W, 3.2A
Maximum flow rate: 15 m3/h
Maximum pressure: 15m

I don't have a fancy water test kit as they are impossible to find here in Bulgaria so i've been using the red / yellow liquid test kit which measures Chlorine and PH level
we have a few neighbours here with similar pools and this is what they use with no issues. I check the chlorine / ph levels weekly and add granular chlorine or Minus ph as required

We keep the Free chlorine at between 3 and 5 ( i assume that's PPM?)
and PH 7.5

When we bought the house the pump had been stolen and the pump house and electrics were underground and were in a shocking state so we replaced everything and moved pump and filter above ground.
We removed the sand in the filter washed and put back.

All was good with pool between june and July crystal clear water and chem levels constant, the only thing we noticed that was after a heavy rainfall the PH level would rise so we added minus ph to bring it down.
Then mid August air temp rises to above 35 and close to 40. Water temp reached 35 at one point and at the same time green powder started to form on bottom of pool. we looked online for help and followed instructions
(half emptied pool, shocked with chlorine etc) but nothing worked. vacuumed pool every day and backwashed filter daily but pool would just go cloudy and green powder returned next day. We didn't have a summer cover in place
and it gets quite windy, we are also close to the coast so we assumed it was fine sand getting into pool and decided to empty pool for the summer with clean water and start again following year with a pool cover in place.

So this year we started from scratch, jet washed the pool and re filled, bought a summer cover to keep debris out when not in use . All good until exactly the same time in August!
Green powder forming bottom of pool, went through the same process RE shocking but to no avail. After a process of elimination i decided it must be a sand filter issue so i emptied the
Sand and lo and behold it was bright green and disgusting, So We replaced the sand in the filter with one recommended by a pool supplier its 0.25 mm = 0.5mm (granular size)

Ran the pump and lo and behold the pool cleared up in 24 hours! christal clean again and the wife was happy. Alas this lasted about 3 weeks and now its gone back to green algae yet again.
We are at our wits end. So now after some research i think maybe the sand in the filter has become "channeled" due to the pump being too powerful?

We have decided to close the pool for the winter, but we are not going to empty. And next year change the sand in the filter to the more expensive silicon
type which allegedly does not have issues with channeling? or should we get a smaller pump? (the pump is one speed and cannot be regulated).

Any comments or advice would be appreciated.

Many thanks Reggie

Welcome. The filter is not the issue, it’s that there’s not enough chlorine in the water. Cleaning the sand just got rid of the visible algae but without chlorine in the water it just grows back in a couple weeks.

A few things: you need to know how much stabilizer is in the water. If there’s none, the chlorine you add will be gone in a few hours. If there’s too much, the chlorine that’s there won’t be able to sanitize the water. So find a kit that can test CYA/stabilizer.

Chlorine needs to be maintained at the levels in the attached chart here:

Chlorine/CYA Chart

EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...

www.troublefreepool.com

Be aware that trichlor/dichlor tablet forms of chlorine add chlorine and CYA. As the CYA goes up, you need more chlorine to keep the water sanitary so those are not long term sustainable unless you replace the water frequently. Liquid chlorine tends to be the best option if it’s available or a salt water chlorinator is good as well since neither of those add extra stuff to the water.

 

[Regmcm]

Thanks for your reply, At the moment i cannot test the CYA levels as i done have the testing kit.(im going to order a better testing kit but it might take 2 or 3 weeks to arrive as they are not available in Bulgaria. However the Cholrine and PH levels have been maintained at a constant level throughout the season. FC around 5 PH 7.5. My thinking around the problem being the pump or Filter sand id that our direct neighbours have similar pools and have never had an issue with Algae. They are maintaining levels the same as mine. The only differentiator between theirs and mine is that i replaced the pump as the original was stolen and replaced the filter sand. (which cleared the pool completely after 24 hours)

What would cause the CYA levels to change? Rainfall? hotter weather? the environment? pool usage? I have also been using the slow dissolving tablets in a floater (chlorine PH and Algae treatment) Until i can test the CYA levels

Can you also advise if the pump i have is overpowered and if it is, could this be the issue? (creating channels in the sand?) This morning i have cleaned out the filter and replaced the sand, will leave pump running to see if this makes a difference.

PS how do i change the CYA levels? is there a chemical i can add to increase/ decrease ?

Again many thanks

 

[TinFoilHat]

Different pools are all going to take different approaches to keep them sanitary. Yours simply has not had enough chlorine for the chemistry that is in your water. You should get your hands on some liquid chlorine and put 5 ppm of it into your filtering pool every day until you can get a proper test kit that can measure chlorine with the FAS/DPD method. Stabilizer or cyanuric acid (CYA) can be added as a granular or liquid but only use liquid if you need to use the entire bottle as it separates in the bottle.

 

[Bperry]

Thanks for your reply, At the moment i cannot test the CYA levels as i done have the testing kit.(im going to order a better testing kit but it might take 2 or 3 weeks to arrive as they are not available in Bulgaria. However the Cholrine and PH levels have been maintained at a constant level throughout the season. FC around 5 PH 7.5. My thinking around the problem being the pump or Filter sand id that our direct neighbours have similar pools and have never had an issue with Algae. They are maintaining levels the same as mine. The only differentiator between theirs and mine is that i replaced the pump as the original was stolen and replaced the filter sand. (which cleared the pool completely after 24 hours)

What would cause the CYA levels to change? Rainfall? hotter weather? the environment? pool usage? I have also been using the slow dissolving tablets in a floater (chlorine PH and Algae treatment) Until i can test the CYA levels

Can you also advise if the pump i have is overpowered and if it is, could this be the issue? (creating channels in the sand?) This morning i have cleaned out the filter and replaced the sand, will leave pump running to see if this makes a difference.

PS how do i change the CYA levels? is there a chemical i can add to increase/ decrease ?

Again many thanks

How do you chlorinate the water? If it’s with something other than liquid chlorine, then the CYA is added to the water every time you add that type of chlorine. Once the CYA builds up enough, there’s no amount of chlorine you can add that will keep the water clean and you have to drain it. Keeping a constant level of chlorine without knowing what the CYA level is doesn’t tell you much. Algae is always a chlorine problem and not a filter problem.

 

[Regmcm]

How do you chlorinate the water? If it’s with something other than liquid chlorine, then the CYA is added to the water every time you add that type of chlorine. Once the CYA builds up enough, there’s no amount of chlorine you can add that will keep the water clean and you have to drain it. Keeping a constant level of chlorine without knowing what the CYA level is doesn’t tell you much. Algae is always a chlorine problem and not a filter problem.

hi thanks for your help

I am using powdered "fast" chlorine powder (granufast) and adding at the recommended dosage weekly. its really difficult to get liquid chlorine where i live, its almost 3 times the price of powder as it has to be delivered, its not available locally.

 

[Regmcm]

Different pools are all going to take different approaches to keep them sanitary. Yours simply has not had enough chlorine for the chemistry that is in your water. You should get your hands on some liquid chlorine and put 5 ppm of it into your filtering pool every day until you can get a proper test kit that can measure chlorine with the FAS/DPD method. Stabilizer or cyanuric acid (CYA) can be added as a granular or liquid but only use liquid if you need to use the entire bottle as it separates in the bottle.

thanks

So i can rule out 100% the pump being too powerful or the wrong type of sand in the filter? These are the only things that differ between myb pool and my neighbours pool. once i get the testing kit i will test his water as well as mine. cheers again

 

[sande005]

You have one clue - that the sand was bright green and disgusting when you opened the filter. Only one way it gets like that - by filtering out what is in the pool. So it is doing its job.
It can get to the point where it has trapped all that it can. Your pressure gauge is an indicator of that. Backwashing is the normal solution to flush out the accumulation. Sometimes a deep clean may have to be done, but not frequently (Deep Cleaning a Sand Filter) Very rare that one needs to replace the sand completely.

Granufast definately has CYA as an additive. So your CYA level has been increasing, which requires higher and higher levels of Chlorine to be effective. The minimum is the bare minimum. If you are at that level, the odds are very high that you will dip below as the day progresses, and that is all algae needs to start growing. See the chart.

The only way to get rid of CYA is to drain off water, and replace with fresh.

The only effective way to get rid of all the algae is to start with a lower level of CYA, and add non-stabilized Chlorine to get to the levels indicated for SLAM. That will take a lot, and may take days (or even weeks in really, really bad cases).
Basic test kits or strips cannot measure the higher levels needed, hence why we push for a more comprehensive kit.

 

[Regmcm]

You have one clue - that the sand was bright green and disgusting when you opened the filter. Only one way it gets like that - by filtering out what is in the pool. So it is doing its job.
It can get to the point where it has trapped all that it can. Your pressure gauge is an indicator of that. Backwashing is the normal solution to flush out the accumulation. Sometimes a deep clean may have to be done, but not frequently (Deep Cleaning a Sand Filter) Very rare that one needs to replace the sand completely.

Granufast definately has CYA as an additive. So your CYA level has been increasing, which requires higher and higher levels of Chlorine to be effective. The minimum is the bare minimum. If you are at that level, the odds are very high that you will dip below as the day progresses, and that is all algae needs to start growing. See the chart.

The only way to get rid of CYA is to drain off water, and replace with fresh.

The only effective way to get rid of all the algae is to start with a lower level of CYA, and add non-stabilized Chlorine to get to the levels indicated for SLAM. That will take a lot, and may take days (or even weeks in really, really bad cases).
Basic test kits or strips cannot measure the higher levels needed, hence why we push for a more comprehensive kit.

View attachment 608437

Many thanks for your reply. I have a kit arriving tomorrow (its only testing strips but for now thats all i can source) So i will report back with levels. Can you recommend a non liquid form of Chlorine that does not have CYA? (or low levels) I assume if i empty and start from scratch and refill pool next season, and source liquid chlorine, i will then have to ADD CYA ? is there any way of reducing CYA with an additive? (similar to PH minus). thanks for your help!

 

[Bperry]

Many thanks for your reply. I have a kit arriving tomorrow (it’s only testing strips but for now thats all i can source) So i will report back with levels. Can you recommend a non liquid form of Chlorine that does not have CYA? (or low levels) I assume if i empty and start from scratch and refill pool next season, and source liquid chlorine, i will then have to ADD CYA ? is there any way of reducing CYA with an additive? (similar to PH minus). thanks for your help!

There isn’t an alternative. Chlorine is a gas so to make it powder, you’re stuck with CYA(trichlor) or calcium(cal hypo). The calcium has the similar issues as CYA of it builds up you can get calcium scaling. Usually the liquid chlorine is sold as plain bleach.

If you’re using pH minus, that stuff will add sulphates to the water which degrades concrete and metal surfaces. Is muriatic acid available as it’s much safer for the pool.

 

[sande005]

If you empty and start over, ideal would be to add only stabilizer to get the CYA to the level you desire. CYA doesn't occur naturally in water sources, so you would be starting from 0 (if it was a 100% drain of the pool). Then use liquid chlorine as needed.

IF you can source a recommended test kit, you can use combined chemicals to get to your CYA goal after refilling. That requires repeated testing so you always know where you are currently at.
Start with a little stabilizer only to begin with a level of 20 for CYA (to avoid a harsh feel, and to give some protection from sunlight).
Use stabilized Chlorine (tablets, Granufast, etc), but then stop using once the CYA is at the level you want, and switch to non-stabilized.
If liquid Cl is really impossible to get, you could test for CH, and if the initial is low (~250 ) use cal hypo powder to sanitize. It would slowly raise your CH levels (but no CYA), so you need to stop using when it gets above 650. (Ideal range is 350-550 for a concrete pool).
So a balancing game between the two forms of Chlorine. Eventually you will get to a point where you can't use either - and if there is no liquid available, you need to drain the pool again. But that might get you a year or two - all depending on the actual results and how much of what you have to add. Always refer to the chart above, as your target for Cl will be increasing as the CYA increases.

I found one of many sites that say they ship liquid chlorine to Bulgaria. No idea as to how reputable they are, or what the cost to you is (inexpensive? very expensive?). Here's one: 1 Case of Liquid Chlorine Pool Shock - Commercial Bulgaria | Ubuy

Using liquid only has the downside - you have to test and add frequently (daily, maybe every other day if lucky).
The ultimate is to switch to a Salt Water Chlorine Generator - you add plain salt to the pool, at a fairly low level. The generator then makes Cl for the pool, which later recombines to salt, which again becomes chlorine. So no adding of chems. And you can keep the CYA and CH at their levels independently with no build up. You may have to test Cl periodically, and adjust the levels generated if needed, but it will be far less than any of the above.

All of the above aside - since you do have algae growing, even with a complete drain of the pool, you will still need to do a SLAM process when refilled, to make sure any remaining algae is killed. It may not take as much Cl, or have to go on very long - but is still critical to prevent regrowth in the future. Salt generators are great for maintaining a level, but cannot generate enough to get to the levels we recommend for a SLAM process.

 

[Regmcm]

Thanks Sande, I will check out the link i finally got my testing kit, here are the results .

Alkalinity 60
PH 6.8
Free chlorine 0
Total Chlorine 1
CYA between 0 and 30
total harness 500

I must admit i thought my CYA levels would be very high hence the build up of Algae. pool season is over now so i am about to close the pool, But now instead of emptying
i am thinking of winterizing and covering. Then slam and adjust levels next year?

Any advice would be appreciated!


Reggie

 

[sande005]

You algae is due to the low CYA and no, or almost no, FC. Go ahead and add enough Granufast to SLAM levels for a few days before you close to knock down what you can, and inhibit new growth for a time while it is closed. That will bump your CYA some, but there will be some reduction over the winter. Open in the spring as early as possible, algae will grow in really cold water, but at a much slower rate. And with the low temp, and initially lower light, your Cl won't get used up as fast - so less liquid to add to maintain a SLAM to kill off what is there.