forgive me if this is old ground but, i cant seem to find a previous thread on this. i recall readine somewhere that water features and other aeration can impact pool chemistry (maybe TA and CH). if this accurate and is there a good rule(s) of thumb?

Aeration raises pH without affecting TA. The act of lowering the pH with acid lowers TA, so I guess you could say that aeration indirectly affects TA. It does nothing to CH, unless you count the greater evaporation causing you to have to add water and thusly add Calcium, and since calcium doesn't evaporate your CH rises.

Wow, was that clear as mud??

Maybe its me buy that was clear! So running the waterfall could offset some ph lost to tricolor. At least a little.

Correct, just keep an eye on your TA. The pucks will lower PH and TA, while the water features will tend to make PH rise (offsetting the pucks) it has no effect on TA, so eventually your TA will get too low and you'll need to raise TA up with baking soda.

That said, when using trichlor, also keep a sharp eye on your CYA level.

Trichlor tabs are not a good choice as a primary chlorine source. They are very acidic and they add a lot of cyanuric acid. For your 30,000 gallon pool, every 3-inch trichlor puck (7 ounce) will increase the cyanuric acid by 1 ppm. Every ten pounds of trichlor will raise your cyanuric acid by 22 ppm.

Liquid chlorine would be a better choice for your primary chlorine source.

Thanks for the insight and I have been considering moving off of triclor. It is just so darn convenient. If I do that, roughly how often would I need to add stabilizer given my other values?

I usually add a little CYA only once a year, right after open. I don't have to add any the rest of the year unless we have a monsoon and lose a lot of water due to overflow. I run mine about 60ppm or so.

If you have evaporation, and add water to refill the pool to the proper level, and the water you add has a lower CH than the water that is already in the pool, will it lower the overall CH of the pool?

No, it will still increase. Evaporation has no affect on the amount of CH in the pool. Think of it in terms of actual weight/volume instead of ppm.

So if you had, say, 1 lb of Calcium in the pool and 2% of the pool evaporated, you would still have 1 lb of Calcium. Even when you add water that is pretty low in Calcium, you are still adding some to the total so your CH ppm would increase.

What if you drained 2% of the pool water and replaced it with water with zero calcium? Would that lower the CH?

Draining is completely different than evaporating. Draining will lower CH as long as the fill water doesn't add it back.
So the short answer to your question is, Yes!

You may also need to be aware of the TA of your fill water. In my pool, the spillover spa and the waterfall tend to drive up pH and also increase evaporation.

When I add water it has a TA of about 340. So even a regular 1" or 2" per week will increase TA. So the pH rises even more. So, I add MA as often as I add chlorine.