Dark Green Matter: When to Drain the Pool

"3 inch thick, lumpy green mashed potatoes" is how I described the algae bloom that devoured the surface of my swimming pool while I was away on a 10 day vacation...with a dead bird, squirrel, and chipmunk.

Rewind to 10 days earlier when I made the executive decision to leave my pool filtration system off and the pool uncovered for the duration of my vacation. How bad could it get, I thought, as I pulled the plugs to drain my equipment. Well, I found out.

BUT STILL, as bad as that was, I didn't have to drain my pool water. With a concisely calculated pool chemical plan of attack, I was able to restore order in my pool in a couple of days. It's always a last resort to drain your swimming pool. Whether it's a bad decision like I made or simply just that nervous day when you pull back your pool cover for the first time in the Spring - it's important to be able to discern when it's time to throw in the proverbial pool towel vs. when it's time to reach for your stash of pool chemical weapons.


1. Can I See the Floor in the Shallow End?

If you can see even the faintest hint of the shallow end of your pool floor there is hope. With You will need a well operating filter, running as much as possible, and lots of diligent cleaning and brushing. You'll also need proper water balancelots of shock and other helper chemicals. No matter where you live and how big your pool is, it's probably going to be cheaper to purchase these pool supplies than to rack up that water bill. It also takes a little patience, requiring 1-2 weeks of daily attention to the pool water.

2. Can I Manually Remove This Debris?

I previously mentioned the belly-up critters in my pool. I was definitely questioning whether to drain or not to drain due to... I don't know - fear of the plague, maybe? If there was one more or if they were larger animals I don't know if any amount of shock could sanitize the germs. Birds are one thing but what about heavy debris in a pool neglected for months, or left uncovered all winter? If your pool is covered in a foot deep of leaves that is too much for you and a Leaf Rake, and you have cannot vacuum to waste (hi, cartridge filter) - it's probably a good idea to start fresh, or call in a pool company to use their portable vacuum equipment.

3. Can My Pool Filter Handle This?

If you have a small sand or cartridge filter and you were wishy-washy with your answers to the first two questions it is probably best to drain the swamp. If you felt pretty good about your chances when questions 1 and 2 were posed to you and you own a large DE Filter - you still have a fighting chance. Small filters may be adequate for good water conditions, but can be overwhelmed by very 'thick' water. And, severe algae clean-up with a small filter can often spoil filter sand, and ruin filter cartridges. IF you have a large and/or effective pool filter however, you're good to go!

4. Can Your Filter Run 24/7?

Ok, so this 4th question is really a series of intermingled questions that pertain to your neurosis. Can you run the filter pump 24/7 without it bugging you? Some people just can't sleep at night with a pump running outside their bedroom window, or in some cases loud pool pumps generate complaints from neighbors. Perhaps you hear a faint sound of money cha-chinging it's way out the window as your utility bill spikes. Maybe you don't trust modern engineering and are concerned about something exploding out there.

Consider the options and make a choice; boost the electrical a little bit or boost your water bill by 20,000 gallons? Running your pump and filter non-stop for a few days or a week may be necessary. Run a DE filter for only 22 hrs daily, to allow the DE and dirt to slough off the grids and mix-up.

5. Pool STAINS !?!?

Sometimes being a pool owner is a hard knock life. The very word "stains" can bring pool owners to their knees with a bucket of soap and bristle brush. Draining and cleaning allows you to acid wash (plaster pools only), to brighten the finish and remove stains. Dark green pools that are not drained and cleaned often have stains all summer. Bummer. Yet, there are plenty of pool stain chemicals for any kind of stain you can think of. So although you may bring the water back to blue, the pool floors and walls may not look so hot. You can use Stain AwayJack's Magic or Stain Free, along with well balanced water, to remove most pool stains left by debris and algae.

6. When's the Party?

This actually happened to me last week. I opened my pool a week late thanks to lousy weather, and it put me under the gun. Instead of two weeks to clear up the quagmire that was lurking beneath my safety cover I had only 7 days. In your case, do you have enough time to ever-so-patiently follow the directions of each chemical, show restraint by not overdosing the pool, and give the pool some daily love? It's not permanent - your pool will come back. If you need to correct conditions as fast as possible, and you would rather pay extra to avoid both irritated guests and fussing with the pool, then go for it and drain and clean the pool! Unless of course...

7. Is there a Water Ordinance I Need to Abide?

Hold on a second there, party animal. Be sure to check with your area's water ordinances. Water is a precious resource and in some areas it's more precious than others. Look online for your city, county or town's rules on draining pools or discharge regulations. Some areas have laws on what days of the week and hours of the day you can use your sprinklers let alone when you can fill up that giant vat in your backyard.

In many cases, a partial drain will get the job done. If you have a main drain and a sand or DE filter, you can close the skimmers and pump the pool down (on backwash or waste) to about 3" from the shallow end floor, then fill it back up again. This removes half of the problem, with half the water cost, and no worries about the liner shrinking or relaxing, or hydrostatic pressure under the pool.

For my pool, after a good floccing, vacuum to "Waste" as thoroughly as possible and then let it continue to run for a few hours. This is a productive way to lower your water levels and to get rid of the finer particulates that are fogging things up. A simple topping-off of fresh water has restored the brilliant blue hue of the previous summers.

I hope these questions answer your questions about the need to drain your pool or not when it comes to algae and staining. Patience, persistence, and trusting the process will get the job done if you have the right chemicals and equipment.

In The Swim makes every effort to provide accurate recommendations based upon current ANSI/APSP/ICC-5 2011 (R2022) standards, but codes and regulations change, and In The Swim assumes no liability for any omissions or errors in this article or the outcome of any project. You must always exercise reasonable caution, carefully read the label on all products, follow all product directions, follow any current codes and regulations that may apply, and consult with a licensed professional if in doubt about any procedures. In The Swim assumes no legal responsibility for your reliance or interpretation of the data contained herein, and makes no representations or warranties of any kind concerning the quality, safety, or suitability of the information, whether express or implied, including, without limitation, any implied warranties of merchantability or fitness for a particular purpose.