Okay I agree, except of course if you are trying to dilute something bad in the water.

I enjoy doing my daily water changes in my 24 gallon:) I've been doing daily 1 gallon water changes and a weekly 4-5 gallon water change on my 24AP for the last 9 months. It comes out to about a 50% total water volume changed per week and I haven't seen any ill effects. It's actually a lot less shock on the system than doing large 50% water changes once a week.

I have about 35lbs of LR and 20lbs of LS, along with all of my corals and 3 fish. I test my water weekly and still have to dose every other day Ca,Mg, Stontium, iodide, coral-vite, trace elements, and buffer when I need too. I know that many people think the water changes are enough, but I tried and my corals consume sooo much. Regarding the Strontium and Iodine dosing. I just do about half the recommended dosing and I could tell by seeing how my corals react that it's a positive or negative effect. I also have at least 15 gallons of mixing water, just in case there was an accidental OD. Haven't had one yet and so far it's been working for me.

I decided to start doing the daily water changes after moving my tanks back in August. My 95 gallon I only do a 30% water change every other week and it seems fine, but I do notice that it has more water quality issues than my 24 gallon. It's mostly because of the fish bio-load due to three large tangs, but my kids like them. It has zoas, palys, clams, nems, toadstools, mushrooms, frogspawn, and other softee and LPS corals.

My 24 gallon is a mixed reef of SPS, LPS, and softees. I do overfeed my tank and I don't have a skimmer, so that's why I decided to keep up the water changes. I feed Phyto, Oyster, Roti, Arctipods daily, and mysis to my LPS and fish every other day. I also dose Brightwell Coral Amino's 10 drops daily. My water changes only take me 5 minutes and my water consistently reads as follow.

SG 1.025
Ca:420-450
Mag:1300-1350
Alk:9
PH:8.3
Ammonia 0
Nitrate:0
Nitrite:0
Phos:0

The daily small water changes has been the best by far. I haven't seen any swings in any of my numbers and my water is always crystal clear. I get excellent polyp extension and growth from my SPS, LPS, and softees. Even the corals that require "dirty water" like xenias, zoas, acans, etc. are doing great along with my SPS corals. I'll try to get some updated pics later.

If he keeps hard to kill softies like shrooms and hardy fish, it likely won't bother anything. Just a big fat waste of time. Otherwise yes, you are correct. A 50% water change to a typical reefer is usually only under taken only under emergency conditions because we all know it's brutal on a lot of LPS and virtually all SPS.

Assuming you have a tank with a large bio load a big water change will cause nutrient levels to go all over the place and stress anything with a hard skeleton. If you aren't using RO water than you are likely dumping mass amounts of phosphate into the tank as well.

My regiment is 10% weekly, with calcium and buffer suppliments between. Also, my main frag tank has NO fish or inverts in it, and I actually add nitrate from my fresh water tank to keep the level at about 5ppm. The extra nitrate helps growth, and doesn't bother my acros in the least.

A few years ago I tried an experiment with a tank that had no water changes for 4 months and using the suppliment only approach. No fish or inverts in the tank so nitrate was zero to start and zero to end. It didn't work. After about a month the tank started to deteriorate and growth eventually slowed to nothing. Then stuff started going backward. I concluded that obviously nutrient export isn't the only reason to do water changes.

There's a lot of theories on this, some rather weird but some make tempting sense. A big belief is that enclosed aquariums become screwed up ionically after awhile because of the constant circulation of water agains't plastic and inert surfaces. In the open ocean you have interaction of waves, rain, and influx of cold water currents from the poles. The addition of freshly mixed water, even a small percentage to a tank simply does more chemically than add trace elements from salt mix.