As one can tell from this thread, this is a near religious issue for some on both sides.
From what I've learned reading lots of threads and books:
- Sometimes there's an easy answer: if I'm doing a pico or small nano, then just do daily-to-weekly 100% changes because they're easy. But if I'm doing a 100gallon tank, 100% weekly changes are much much harder.
- If something bad happened in the tank, I'll need a water change ASAP.
- If I'm using the Triton system, or the ATI essentials system (my choice), they say don't do water changes.
- If I'm doing the Red Sea system (foundations, trace elements, nopox, and all the test kits), it says do a weekly water change.
I am a fan of systems because smarter people with lab experience are behind the whole thing. Each of these three systems, and several others, are used successfully by many people.
What if you're not running any of those systems? (lets say I'm just using Baking soda, dowflakes, and epsom salts) Or, put in a different way, what is the basic logic behind them?
I come to this as a beginning Acropora keeper, based on book and forum understanding but without signifcant practical experience.
I need to keep things as stable as possible, to a set of parameters.
Therefore, if I'm trying to keep things stable,
it seems to me that I need to pick a salt mix that meets my goals, and dose baking soda and dowflakes to keep alk/cal/mg at the salt mix's levels.
I think this might be the most critical point.
- If I don't keep the big 3 at the salt mix's levels, then I'm honestly wasting my time doing water changes, because my big three will always be changing. They'll change between water changes, and then change again when I do the change.
I need to measure those paramaters. I think these days that means, like the Triton/ATI methods, fairly regular alk tests, other tests as needed, and seasonal ICP tests. This tells me a huge amount.
This also assumes my feeding and nutrient export is
balanced (not necessarily low feeding, though doing this by low feeding is far and away the easiest) to keep nitrate and phosphates at a low level. If you can't keep this under decent control, water changes might be necessary. I would also argue that you might not be ready for an acropora system.
Then there's the question of trace elements. If my tank has a strong appetite for, say, strontium, I will have it constantly depleted and variable, even if I do water changes, unless I do a 100% water change frequently.
But this brings us to a different point: I believe the best practice for water changes is to do roughly weekly water changes of around 10% (+/- a factor of two for either time or amount). If you do too much, you again unbalance things.
In that case, with our strontium will
always be chronically depleted unless i detect that it's being consumed so much, and supplement it.
I can get around that by lightly dosing a WAG amount of the trace element formula of my choice, and basically trust the manufacturer when they say "use 5ml of this per 10 gal per week (or whatever) to keep trace elements at good rates". Hopefully, ICP will help me correct any errors I make.
Note that at this point I might as well be doing one or another of the Triton, ATI, Red Sea, etc. systems.
(as an aside, a soft coral and/or photosynthetic gorgonian tank where they don't mind, any may appreciate, elevated levels of nitrate and phosphate, might not mind swings in these parameters, and where they might not be picky about trace elements, is a completely different ball game than the way I understand acropora keeping. Same thing might go in a mixed softy/gorgo and macroalgae tank;
in which case fairly frequent changes, up to maybe 50% a week, probably, based on my limited understanding of such things, be good to get out all kinds of organics. Running such a tank with water changes only and no supplementation may be viable)
In summary, I see only a few courses of action, based on my understanding of acropora care:
- replace the water 100% very frequently (say weekly at the most); so that in the intervening time there's little chance that the tank's parameters will become too different from the fresh saltwater. This option is viable for tanks under 5 gallons, but I think a bit of a chore for tanks over 10 gallons. (or, if you live literally next to the sea, you can automatically pump it into a holding tank. I think that would be cool; and if I were in such a situation I probably do at least daily 100% changes.) This *may* be the healthiest option overall.
- run one of the systems mentioned above, or another brand of your own choosing. And don't do it willy nilly; run it lock stock and barrel.
- DIY your own system, to match your chosen natural/artificial sea water (otherwise, all your supplementation and water changes, it seems to me, is useless). I don't see how this gets around the trace element problem, unless you just want to fire and forget with a certain brand of trace elements, and/or if you want to believe that most trace element monitoring/supplementation is snake oil.
My choice was #2, and I'll start ATI essentials in a week or so once I have a good guess as to what my daily alk consumption is.
Again, if you're running corals that don't mind modest shifts in Nitrates/phosphates and don't care too much about trace elements, it's a whole different ballgame.