Hi Folks,

We live in Southern Maryland and have the following:

20' x 48' gunite pool
36,000 gallons
Jacuzzi tri-clops filter
Jacuzzi pump (3/4 hp I believe, I can confirm this if important)

We had a local pool company open the pool June 15; the water was clear, but there was a heavy algae growth on all sides and bottom. They added 5 lbs of dichlor at opening; we have used dichlor as our pool shock for several years with no problems. I put two 3-inch chlorine tablets in each skimmer and brushed the pool. The walls came clean but the water turned into a green mess.

I have been running the filter 24/7 and have had to clean the filter cartridges after 12 hours of filtration due to pressure going up 10psi (filter cartridges are covered in algae each time I changed them). I have 2 sets of cartridges, but it is a pain to change them out and clean the cartridges 2x a day.

The water stayed green through the weekend and we had the water tested June 18. The CYA was over 160 and I was told to drain 60% of the pool and refill with fresh water. We are on a well, so there is no way I could drain that much water at once, so I have drained about 2 inches of water the past two evenings and and added water via the hose to replace.

We had the water retested today; the pool company did some additional tests and here are our results:

free chlorine - 0.37
total chlorine - 0.88
combined chlorine - 0.51
ph - 7.47
hardness - 161
akalinity - 115.03
CYA - 163.62
copper - 0
nitrates - 80
phosphates - 50

The test printout today recommended a 90% drain of existing water and replacement with fresh water.

Is there anything besides a full drain and refill that will fix our pool water? If not, do you recommend that we gradually drain and replace the existing water with fresh? Should I bite the bullet and drain the whole thing and start from scratch?

I am concerned about potential "pool popping" as there is a lot of clay in our soil; we have a 6' fence around the pool and one of the fence posts "popped" last year and I don't want to risk having the same happen to an empty pool. Pool trucks in our area can deliver a max of 6,000 gallons at one time; would a drain and refill of 1 truckload every couple of days be a good way to gradually add the water if we don't go for a complete drain and refill?

Also, should I try adding lots of liquid chlorine (generic store bleach) to the pool at this point to try and get the CYA and the chlorine lined up to hopefully kill off some of the algae?

Please let me know if any additional info is needed and thanks in advance for your advice!