What do you put in your RO???????

Top off water should not have a real measurable pH. Technically, it should be 7.0, but atmospheric carbon dioxide will quickly dissolve in it, dropping it well into the 6s. If your top-off water is measuring 7.7-8.0, then your RO unit isn't doing its job. If you are referring to premixed artificial seawater and not top off water, then the above also answers that question. Buffer will not significantly help, since the pH will drop again shortly thereafter due to carbon dioxide solubility--in fact, you'll increase the total amount in solution that way.

Sure, there's chemistry involved. However, the only chemistry occurring is some addition of very weak acid in the form of H2CO3 from dissolved CO2 and some dilution. That's it with RO water. Keep in mind that this weak acid does not really affect alkalinity to any appreciable degree, but will depress pH. But basically, nothing happens with the addition of pure water, minus a drop in salinity (which is the effect of dilution) or a very insignificant drop in pH (we're talking tiny here). Basically, the reason it doesn't affect the chemistry so much is because there isn't really anything in it that would affect chemistry. So, no, there is no need to buffer your top off--buffering your top off could actually cause some calcium-alkalinity balance issues.

Nah, no reason to hide . It is actually a very common assumption/misunderstanding. If you want to raise the pH in your main tank, there is one additive you can use in your topoff water, called kalkwasser ("limewater," literally). It is a balanced calcium/alkalinity additive that has the added potential benefit of raising pH. The only caveat is that it must be added very slowly (in a drip-wise fashion) to keep the pH from skyrocketing.

I buffer my top up water, my tank uses around 15 litres of top up ro a week and my alk always sits around 9.6. My calclium is always between 420 and 430 and my ph a steady 8.1 (drops to around 7.96 during the night).
My ph used to drop a bit due to the decreasing alk levels during the 7 days I work away, this has solved my problem as I'm not there to add manually with no adverse effects. I know quite a few people that buffer there top up water.

I dont alter my RO/DI water when adding.