water change question

[Amadod2]

in the past i use to do weekly 10% but was told that wouldn't help the tank because it was too little and too often, . so now i have been doing 30% every three weeks and i been told its too much and the corals won't like that. i want to get into a routine that will not be hard so i can continue to do it and that the corals will thrive over time. i was thinking of doing a 10G water change every two weeks on my 75G as the actual water volume for the tank would be roughly 70G or less so it works about to be a 15% water change. what do you guys think??

[Animal-Chin]

My sps don't like big changes and here is why...

I carbon dose with biopellets and a reactor. Because of this I keep my alk at 7 as any higher and my acro's burn their tips. So I have a dosing schedule that keeps my alk steady at 7 all the time.

My salt mixes WAY higher than that. I've measured my instant ocean alk at 13 before but its always higher. If I do a larger water change (say 20%) my alk will swing that day to 8 or 9 and the next day my acro tips will burn. It will drop over the next few days though.

Considering I run a phosphate and nitrate reactor my main reason for water changing now is to add trace elements back into the water. For me doing smaller weekly changes accomplish this and don't create the alk swings I'm trying to avoid.