Carbonate Hardness Dropping

[sen5241b]

Checked my KH a few days ago and it was 107 ppm KH. Just did a 20 to 25% water change and it dropped to about 89 ppm KH. I thought water changes would raise KH. The tank is about 17 months old and the other chems are fine. Ph about 8.2, calcium is over 400ppm and magnesium is approx 1100 ppm. Salinity 1.020. What gives? More water changes?

 

[yote]

What brand salt are you using?

 

[RyanG]

Running a DSB by chance? That seems to be one of the precursors to bad things if you are.

 

[messiah023]

How much over 400ppm is your calcium?
If your calcium goes high, your KH will go low.
My thoughts are to double check your calcium level (preferably with another test kit, like one from your LFS).

My calcium kit was reading about 450ppm, but all my corals were beginning to close up. Took a sample to the LFS, it was off the charts and my kh was extremely low.

Purchased some Kent DKH.
Small dose over 2 days brought everything back to normal.

Good Luck.

 

[mblack]

test your change water before adding it to the tank to make sure that's ok.

I would say your magnesium is on the low side, you should aim for between 1250 to 1400ppm, ideally at 1300 to 1350ppm. A low value for magnesium will lower your KH for some complicated reason I don't understand!

I would start by raising you mag to within the range above. Use epsom salts for a one off supplement, you will need approximately 2 grams per gallon of water in your tank to raise it by 50ppm. I would raise it by 50ppm per day until it gets to 1350ppm.

After your mag is correct, retest the KH and then if it is still too low, which it probably will be, look to buffer it. If you try to raise the KH without fixing your mag levels it will probably go straight back down.

Hope this helps

 

[sen5241b]

I use Oceanic salt. I'm going to re-test everything. I do not have a DSB.

 

[sen5241b]

Re-tested everything in my tank very carefully:

Ph 8.3
Calcium 400 ppm
Alk 89 KH
Magnesium 1280 ppm
Nitrites 0 ppm
Nitrates < 1 ppm
Salinity 1.020
Temp 78-79


Alk of my salt mix (Oceanic), is 120-125 ppm KH.

Why then did my alk drop after the water change and why is it low to begin with?

 

[yote]

Part of your alkalinty is made up in magnesium like Mblack mentioned.That being said,you magnesium is a bit low.It should be between 1350 and 1400.
Plus your salinity is a bit low,which could account for the lower alkalinity.Less salt,means fewer buffers.
I'd bring the salinity on up to 35ppt or 1.026sg. which is closer to NSW.

 

[ccCapt]

Salinity 1.020. What gives?

Why is your salinity so low? Bring that up to natural seawater level (1.026) and all your parameters will rise.

 

[sen5241b]

It was low in case my ATO went offline I'd have more time to react but my ATO has never had a problem and stable Ph is more important. thx.

 

[JAG107]

Oceanic salt has lower levels of alk. I have to dose constantly with this salt, which is fine by me. I don't know how you like lots of dosing, though. +1 everyone who said get your salinity up.

 

[sen5241b]

Recap on this issue: alk is to low.
Original tests:
Ph 8.3
Calcium 400 ppm
Alk 89 KH
Magnesium 1280 ppm
Nitrites 0 ppm
Nitrates < 1 ppm
Salinity 1.020
Temp 78-79

I have slowly brought my salinity as per everyone's suggestion up to 1.026 and now my alk is still at 89.5 ppm or 5 dkh. My Ph is now 7.8 !! I only do a 20 or 40% water change once a month.

What's going on with this?! (Jag107, what do you dose with to keep Alk up?)

 

[ndepratt]

If you have pretty stable calcium, you might try a product like Kent's Super Buffer DKH. super easy to use, i highly recommend it for just bumping up DKH without messing with calcium.

 

[yote]

+1 Nathan
Baking soda also works good.

 

[ndepratt]

+1 Nathan
Baking soda also works good.

definitely, great advice, I always forget about that :P

http://www.reefsanctuary.com/forums/reef-chemistry-forum/23076-making-sodium-carbonate-can-fun.html

 

[sen5241b]

What about just changing to a salt mix that keeps higher Alk?

 

[ccCapt]

I really have to question your testing methods or test kits. Your #'s do not match up with what Oceanic should be. On average, a fresh mix should be around 580 ca, 8.5 dKH and 1650 mag. Test a fresh mix and see what you get. It should be very close to those #'s.

Reef Central Online Community - A General Guide to Salt Mixes

 

[ndepratt]

I used to do the "miracle mix"-- IO and Oceanic, worked very well.

 

[sen5241b]

I really have to question your testing methods or test kits. Your #'s do not match up with what Oceanic should be. On average, a fresh mix should be around 580 ca, 8.5 dKH and 1650 mag. Test a fresh mix and see what you get. It should be very close to those #'s.

Reef Central Online Community - A General Guide to Salt Mixes

All my test kits are API. Alk of my salt mix (Oceanic), is 120-125 ppm KH, calcium over 400 and Ph is right about 8.3. Yes, I tested everything twice using precise measurement. I've read other website forums on this issue and Oceanic salt causing low alk is not unusual. See Jag's post. I believe Rcpilot had this same issue. I'll probably be switching salt mixes but after looking at the above article I'm not sure that will help. Maybe I just need more water changes.

 

[ccCapt]

All my test kits are API.

Get a Salifert alk test kit. It comes with a calibration sample so you know exactly what to look for.
Even your mag and calcium is way low for what Oceanic should be.