Question on water change chemistry

[Feivel]

I was wondering if there was a formula to calculate the chemistry change when you do a water change. I notice every time i do a W/C I have to add 3 cups of Mg to bring it back to 1350ppm.

I would like to avoid these swings in parameters and pre- dose my water to match to avoid such fluctuations.

Thanks
Cheers

 

[CoryC]

3 CUPS?!?! of the mg solution in a 2 part recipe or a off the shelf diluted additive? even still i wouldnt add it all at once with your water change. 1350 is ideal but 1150-1200 is ok too, or so i've read.

 

[ritter6788]

What salt are you using? A good reef salt shouldn't cause your magnesium to drop.

 

[mike007]

Thats alot of mag. to be adding to your tank. Something is not quiet right here. What test kit are you using? Take a sample to lfs and have them double check. There is no way 2 cups is correct.

 

[Feivel]

According to the brs calculator, to raise mg 100ppm in 100g using their mixture you will need 806ml (just over 3cups) i have instant ocean regular, reef crystals and DD h2ocean. I usually use one cup reg, one cup reef and 2 cups DD. my last water change was 2 months ago. My parameters have never been so stable. The odd soda ash dosing to raise alk.

Im doing a 10% water change soon and wanted to make sure the proportions are correct and wont swing. I crashed my tank on doing religious 10% weekly water changes. Everything is doing 100% better since ive been dosing and holding off the w/c. Ive seen superb tanks on bi anual w/c. So figured a 2 month trial would be cool. The only reason is to replenish any trace elements i am not dosing for but are needed.

I know there is a formula to calculate this ive seen it. Just cant remember where. ....

 

[Dowtish]

How are you dosing ALK and CAL and MAG? Through dosing pumps or manually?

 

[Feivel]

Manually through BRS calculations. Tests were every 3 days until stability was found. Now a weekly test is sufficient.

 

[hunter01975]

maybe post your tanks test numbers and post your made up water test numbers and see what the differance is to see what your tank is
using and to get a little better help from some of the super duper smart reefers...

 

[Feivel]

So, 10% W/C Should calculate out something like this:
"90/100 X Current Calc Level + 10/100 X New Calc = adjusted Calc....and this formula is repeatable every time you make a change"

Ill test before and after results and see how it compares to that

 

[hunter01975]

By know means do i claim to know very much about this but what i was told is to test your pre made water and then test your tank water and that will tell you what your corals are using up in the tank then you dose for that. you cant really dose for anything if you dont know what your low on and what ur tank is using. well i guess you can but they say thats not a good idea..

 

[Feivel]

By know means do i claim to know very much about this but what i was told is to test your pre made water and then test your tank water and that will tell you what your corals are using up in the tank then you dose for that. you cant really dose for anything if you dont know what your low on and what ur tank is using. well i guess you can but they say thats not a good idea..

Please do not confuse my question,I am not trying to determine a dosing schedule, I am trying to determine the effects on parameters during the routine W/C.

I was doing 10% weekly changes religously, I then noticed my corals starting to look weird and shrink-up. I went out and bought a Mg Test and it was at 1050. I bought some BRS stock (Cal Alk Mg) Brought my parameters to par, (yeah 9 cups of MG over 12 days) But wait, there was a water change involved too that seemed to have lowered my params by 100ppm on the MG... Thats starting to get expensive. I asked my LFS who has a tank featured on reefbuilders, what their secret was, he said a scoop of bio-cal and 2 water changes a year.

Either way, I will do some before and after tests, see if that formula works out(pre-set for 10%), and let you guys know in a bit whats going on,I still have to adjust my salt mix.

100g (75 and 30g) 2 tanks plumbed into the same sump, mixed reef, (30g) Acan Dominated, Lps, Sps, clam, Anemone(x3) lots of frogspawn. GSP, Digitas, mushrooms, i have about 100 different corals (some same species different colors, i.e. green and purple candy canes, Red/Blue/Hairy/Rotten Apple/green stripe mushrooms. 30 different acans)

 

[Feivel]

Heres some numbers. 1.026 salt. Bucket is half reef crystal and half dd h2 ocean. Using red sea foundations test kit, Tank sits at 440-450cal 1440mg and 7.5 alk. The bucket sits at 420-430 cal 1300mg and 10.5 dkh.

 

[beaslbob]

I was wondering if there was a formula to calculate the chemistry change when you do a water change. I notice every time i do a W/C I have to add 3 cups of Mg to bring it back to 1350ppm.

I would like to avoid these swings in parameters and pre- dose my water to match to avoid such fluctuations.

Thanks
Cheers

The good news is there is a formula on the effects of water changes.

But using the diy two part system should be good enough. you basically mix up 3 differnt gallons, one for calcium, one for alk, and one for mag. Then dose equal amounts of calcium and alk when alk drops down. After using up a gallon of the calcium and alk you add 300ml of the magnesium. Of course that is all after you first add whatever is necessary of each to get the tank in balance.

For water changes assume you are doing some scheduled water changes where:

water change=fraction of water changed
replacement water=parameters in reaplcement water
period=equals the period (say days) between water changes
buildup=is the change in parameters between changes.
parameters before water change=the tank conditions before the water change.


and you keep doing those water changes until the parameters just before a water change are constant.

The tank will wind up at:

parameters before water change=replacement water +(buildup)/(water change)

For instance, say you do a 1/10 water change every 10 days and the tank buildsup 9ppm nitrates with replacement water that has 30 ppm nitrates.

The tank winds up at

parameters before water changes=(30ppm nitrates)+(9ppm buildup)/(1/10)=30ppm+90=120ppm nitrates.

my .02