Increasing alkalinity with sodium bicarbonate might be difficult if the pH is already high.
What should you do if you need to increase alkalinity, but your pH is already high? This situation can occur during startups, or when pool chemistry is 'bouncing' for whatever reason. If you have ever tried to dissolve sodium bicarbonate in a pool with a high pH (over 8.0), you will notice it can cloud up the water for a bit...if not severely cloud.
So what can be done? It's actually quite simple.
Lower pH first to just below 7.8, then add sodium bicarbonate to raise alkalinity
The first step is to use the Orenda Calculator™ and find out how much acid you need to get the pH to just below 7.8. Take this acid dose and dilute it a minimum of 10:1 with water in a bucket. It is ideal to dilute acid even more than 10:1. Spread it around the perimeter of the pool.
Then, grab another bucket of pool water and begin to dissolve the Orenda Calculator-prescribed amount of sodium bicarbonate. Add it slowly around the same perimeter you just walked with diluted acid. If you see clouding in the water, slow down and dilute more. Let more water into the bucket if needed. You should be able to get the sodium bicarbonate in and keep the water clear if you do this right.
If you were to add sodium bicarbonate before adding acid, it might not dissolve. It could cloud the water in the high pH of the pool. But furthermore, when you added the diluted acid, it would neutralize the bicarbonate you just added.
Instead, by lowering pH first, you set the stage for the new bicarbonate to dissolve easily. And since the alkalinity was lower before adding the bicarb, it takes less acid to do the same pH correction. If you were to wait until after adding sodium bicarbonate, your acid dose would be higher to do the exact same pH correction....so it's self-defeating.