calcium/alkalinity issues

[forestal]

Hello all. I am in a bit of a pickle with my tank and need some help. Please bear with the longwinded intro as it may be relevant

My 120 gallon tank has been set up for 4 years and i have done weekly to monthly 40% water changes during that time.
I use instant ocean salt, maintaining a specific gravity of 1.024-1.025
Until recently I have used the Hagen saltwater test kit and have not supplemented anything.
I use RO/DI for mixing and for FW topoff - I need 5-10 gallons/week topoff depending on the weather/season.
I keep mostly stony corals and fish, feed moderately to heavy, with a 40g sump/fuge.

when doing monthly water changes my Alk would measure 80-90mg/L (equiv. to ppm CaCO3) and Calcium 380-400. When doing weekly water changes I would get my alk to 90-100mg/L(ppm) and calcium to 400 consistently. My pH remains at 8.2-8.3 throughout this. I did a trial of buffering but with all in the tank growing and doing ok, i chickened out afraid I would screw something up.

Then over the last 6 months as hair algae went nuts, maintenance slipped due to health issues i paid no attention, did not test.
The passion has roped me back in and I test the water- but to my great relief no change from previous.
I have cleaned up the tank, have carbon/phosban running, numbers are the same using the Hagen test kit but now my calcium is 320...ok time to start adding as corals are using up faster

after reviewing the online info on calcium supplementation as well as my budget I decide that Kalk(limewater ) for a low-moderate demand tank is a reasonable method. I want to add this to maintain and hopefully boost a bit my alk and add calcium.

I also decided I wanted a better test kit to make sure I am doing well and got the salifert for calcium/pH/alkalinity.

(interject the fact that although i received a minor in chemistry 18 years ago in college, my brain doesn't seem to work well anymore )

So salifert says Ca = 270 (yikes) and Alk is 4.5meq/L (wait but its supposed to be low not high) ;I remeasured with the Hagen and got 80ppm CaCO3 again and 320,
pH with salifert, Hagen and Seachem is 8.2-8.28

reading I realize CaCO3 is not all that makes up the alk, but I am not adding anything except what is in the salt and food.

According To Dr. Holmes-Farley's writings the range to shoot for is 2.5-4 meq/L or 100-120 ppm CaCO3

any advice other than slowly supplementing with kalk and recheck each day to see where it goes.

Dr. Farley had a great article on how to fix depending on where your ca/alk is and if i am too high alk, it is supplementing just calcium, or am i low on both and just supplement Kalk.

Thanks for any help

[framerguy]

Whew, to techy for me, I'll follow along and learn sumthin'!

[lcstorc]

Well I get lost real easy on this chemistry stull but I have a couple of links that may help.
Calcium and Alkalinity by Randy Holmes-Farley - Reefkeeping.com
Advanced Aquarist's Online Magazine - Product Review: Alkalinity Test Kit Showdown

[AQTCJAK]

My question is on you RO/DI system what are the readings when was the last time you changed those filters they can play a very big part

[prow]

i would add calcium cloride and bring things into balance then start up the kalk. i would also check your Mg levels. i think that should do you. on the buffers yup there are a few not only carbonate but bicarbonate, boron and others. here is a link for ya about ph and various alk sups. Chemistry and the Aquarium

and a little quote from that.

From this data it is clear to see the large increase in pH caused by the addition of hydroxide, and also the significant increase when using carbonate. Bicarbonate, on the other hand, shows the expected slight decrease in pH, but not nearly as much as is found with a strong acid of equal concentration. It is also clear that after sufficient time to equilibrate with atmospheric CO2, these differences disappear, and the pH is the same for all of the 0.5-meq/L alkalinity additions. This is an important result: in seawater in equilibrium with the atmosphere, for a given alkalinity there is a single pH that results, regardless of what was added to get to that alkalinity.

just FYI here is a link on boron. something i dont think you need to worry about but interesting and just might be something you need to look into, dout it but maybe. Chemistry and the Aquarium

[forestal]

i am waiting for my MG, test kit i ordered , i agree i need to test it and tonite when get home will test again , i have been adding kalk as an experiment, but if it looks the same, i agree that prob need to add cacl first until it comes up, i willpost my readings tonite

[bluespotjawfish]

Kalk won't bring them into balance with each other. The directions for my kalk say right on it to adjust the levels first before you use kalk. It is intended to sustain appropriate levels.

[forestal]

well part of the issue is, if the hagen test kit is right, then both are on low side so kalk will work, whereas if the salifert is right (more reliable form what i have read) then i need to add cacl, that's why i wanted to give it a couple days and retest and see where the tank is at

[forestal]

calcium 280, alk 3.5-3.8 and pH now 8.3 after 5 gallons of weak-medium str. Kalk drip over 3 days, so, perhaps my initial alk reading was off...
i will continue to drip and test every couple days to make sure nothing goes out of range

[prow]

yeah those numbers make more sense to me. thats kinda what i was thinking. so i will say the same. use calcium cloride to bring things into balance.

for adjustments once you have things all balanced and everything and using kalk/lime water for all top off, i would switch the CaCl to something like seachems adv. Ca+. it has the right ratios of Mg, Sr and Ca. i also like to use seachems reef builder to adjust the alk and seachems reef buffer for the ph or big alk changes.

FYI. kalk is normally depleted in Mg. so if your dripping kalk you may want to check the Mg from time to time.

more on the FYI. my systems Ca/Alk/Mg demand is pretty high. i have a Ca+ reactor with added Mg media and a DIY kalk reactor. i adjust all water changes so everything is on the high side but with in normals ranges. i still need to dose about 300grams once a week of Mg, yup you geussed it seachems adv. Mg is what use.