No need for additives???

[LifeAquatic]

Someone who own beutiful and mature SPS reef told me that he add no additives at all...
All he do is refreshing 10% of his SW water per week (or at least 30% per month). Nothing more.

Any comments please?

He must mean no additives in addition to CAL, ALK, MAG. There is no way to support a thriving SPS tank with just water changes. No way.

 

[d0ughb0y]

Dustin, your observation is correct, and my initial calculations were incorrect.

it is possible to keep up with just water change, as long as the percentage exceeds the consumption rate.

Just using CA for example.

if a 100gallon tank has 420ppm CA, and the new mix contains 420ppm as well (this can be any amount, higher or lower).

Lets say after a week, the ca drops down to 380 for a consumption of 40. (my mistake in my earlier calculation is that I failed to consider that even removing 50% of tank water, what is left will still contain 380ppm). The minimum amount of water change you need to make is 40/420 = 9.5%.

So it is possible that just doing 10% water change can keep CA at 420.

So lets say you use a different salt mix with CA of 500, then you can get by with a water change of 40/500 = 8%.

but this is based on CA only. Alk should be the same since Alk and CA are consumed in a balanced amount. But mg consumption is actually at a lower rate, so even if the salt mix has a lower than normal mg content, in due time, it can elevate the mg level.

 

[d0ughb0y]

correction to the percentage calculation.

if the consumption is 5ppm per day or 35ppm per week, that leaves 385ppm. so that means we need to make up 35ppm per gallon of water in order to bring it back to 420ppm.

which means for whatever amount of water left, the new water must make up for 35ppm for each gallon of water left. That is in addition to the new water must itself keep 420 ppm for each gallon.

assuming the new mix has a CA of 500ppm, which means each gallon of water will contain 80ppm excess over 420 of ca.

80 * X = (1-X) * 35
X = 30% water change.

so it becomes not feasible to use water change to make up for consumed elements, unless the consumption is really low. only if the consumption is 1ppm per day, then it can be made up with 10% water change.

x = consumed ppm for the week
y = ppm over 420(or whatever your target ppm is) of new water

% water change = x / (x+y)

so if your consumption is 7ppm for the week, and RC has 490ppm, or70ppm excess
%wc = 7/ (7+70) = 9% water change.

 

[RealReef7]

question i just recently started getting into sps, so far i have 3 frags. I do about a 15% water change every week... i bought some brightwell 2 part a year ago and didnt even open it yet... should i start dosing it? my cal seems pretty high at 500 and dkh around 7-8.. my question is when will i need to start dosing and how often should i test my cal/alk? I plan on getting a few frags tomorrow but after reading this thread it almost feels like i got this stuff all wrong. can someone please help me? btw my tank has been a mixed lps/softies for years. 2x400w mh, 4 vhos, 3 maxi jet 1200, 3 koralia 4's, return pump of course.

 

[dublo8]

what salt mix do you use?
I know you said you never check ca level, but curious if you can run a check to find out what it is.

I am wondering if it may be irrelevant to maintain ca at 420, even if ca is 42, as long as there is ca, the corals will consume it.


BTW. I notice all those pictures are from september 2009, how about some more recent pictures of the same pieces and fts.

thanks

I have been thinking about that same question for a while. I dont understand the theory either.