Question
QUESTION: What if your live oak is only 4 feet from pool and is 40 years old.  Have crack in pool and pool guy says we now have to remove tree.  Love tree but can't keep having cracks.  Lived here 15 years and had a crack 4 years ago.  Cracks not next to tree but in middle of pool.  Seems if they kill tree then pool will shift other way.  Any thoughts.

ANSWER: Ok I am envisioning that the tree is on one side of the pool and the crack is in the "middle of the pool" in the deeper water. If so I would not think the roots of the tree are causing the crack. Tree roots grow in the first couple of feet of soil and if they run into a hard surface they will turn with the barrier (pool side). They do not grow down and under the pool, So from how I understand the problem, I would not think this is the case here. IF the tree was cut the stump will decay and leave a space that will need to be filed or the soil may lean that way and possibly the pool side. But I do not think the tree is the problem with the cracking.   

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QUESTION: The only difference is the deep end is next to the pool the crack is where the deep end meets the shallow end.  So maybe because the tree gets bigger it might move the pool up a little because it raised the concrete next to it.  But I have always figured if you take it out it raises back down.  Good to know it is not because of roots going under the pool.  

They are thinking about killing the tree and then putting something into the stump of the tree to kill it fast so it would settle before we fix the crack.

Answer
With the information I have and not seeing the crack or the tree location. I do not think the tree is causing the crack. But if you feel this way and you can see the situation then remove the tree. I would grind the stump below the ground surface and let it decay normally.  Depending on your location this can take a couple of years to many tears for the stump to decay. This slow decay will not leave the void and the possibility of the pool shifting would be almost nil. There are products that will speed the decay if you want to go that route.

To enhance decay conditions, the stump should be ground down below the level of the ground, covered with sod and kept moist. During the first year following tree removal, the organisms that decay the wood tend to be nitrogen-limited. That means that the addition of fertilizer during the first year, especially a high nitrogen fertilizer, will hasten decay. The organisms that come along to decay the stump after the first year or so tend to be carbon-limited. That means that adding high nitrogen fertilizer no longer hastens the decay.


Depending on the size of the stump and the possible void it may leave I think once the tree is removed the pressure, if there is any, by the roots on the pool will be gone. I would not kill the tree but cut and remove it alive. Dead trees are more difficult to remove and can be dangerous. I hope this helps. Without seeing the tree I am limited