I have just joined this forum and happened to come across your thread. I want you, and everyone else reading this to know that there is a much, quicker, more efficient and cost-effective method of clearing a green pool than most would lead you to believe.
I have read this sites section on defeating algae, and while I appreciate the effort these guys put in, I disagree with almost everything they have said.
For starters, liquid chlorine is certainly not more effective than granular. Most liquid chlorine has an active constituent of 12.5% Sodium Hypochlorite. Granular chlorine on the other hand, particularly Calcium Hypochlorite, has a chlorine concentration of 70%. Secondly, the "SLAM" method is completely unnecessary and a waste of valuable time/money. I will explain this later.
Let's get right to it. When clearing a green pool, there are three chemicals you need:
-Chlorine (Calcium Hypochlorite)
-Algaecide (Benzalkonium Chloride)
To address the purpose of using these chemicals:
1. Calcium Hypochlorite is the best choice for treating green pools as it has a very high chlorine concentration. It is fast dissolving and very fast acting. Also, it does not affect your CYA.
2. Benzalkonium Chloride is a non-copper based algaecide. It is cheap, effective and does not last in your pool for more than two days.
3. Floc. This is a no brainer and I'm very surprised the owners of this site have made little to no mention of it. This chemical combines all the fine particles floating in the water together and drops them to the floor of the pool, allowing you to vacuum your pool with greater ease.
Now I will explain my much quicker method of clearing your green pool. Note: I am assuming your pool is 20,000L.
Step 1: Brush the walls and remove as much sediment as possible.
Step 2: Turn the filter on to Re-Circulate. if you have a Cartridge filter, simply remove it and turn the filter on.
Step 3: Add 2kg of Chlorine.
Step 4: Add 2L of Algaecide.
Step 5: Add 1L of Floc.
Step 6: Leave the filter running on by-pass for a further 30 mins.
Step 7: Switch the pump off and leave off overnight.
Step 8: Return in the morning and vacuum all the sediment on the bottom to WASTE. If you have a Cartridge, filter the sediment and hose down every 10-15mins (depending on the size).
Step 9: Rebalance the pool chemistry.
Step 10: Viola. You have cleared your green pool in less than 24 hours.
Notice how there was no need for continuous filtering and backwashing. In fact, there was no filtering or backwashing at all. There is absolutely no need to run a filter while clearing a green pool. Also, chlorine on its own is not an effective product for fighting present algae problems. Note how it requires many gallons and non-stop filtering to kick in! It is very important that you use an algaecide as well. Just ensure it is not copper based. It is not necessary to balance your pH or TA levels before commencing a green pool treatment. Chlorine has a pH between 11 and 12. SO, say you add acid, test your pH and it's now sitting at 7.2... great! Then you go ahead and shock the pool. Guess what? The pH is lost already. So what was the point?
So you see, those who tell you there is no magical overnight cure for a green pool simply do not know what they are talking about.
I encourage you to try this method the next time you have a green pool. I guarantee you will find success.