Alkalinity dropping rapidly and inconsistantly

[fishfreak0114]

Hi everyone.  I've been having some problems with low alkalinity over the past while (a month?  Two months?), and have been posting about it on my build thread, but it's time to get a wider spread of opinions on this.  My tank is a 2.5 year old biocube 29, biweekly water changes of 16l with RSCP.  The tank has softies, LPS, and several types of macro.

 

I tested alk a while back and it was at either 5 or 6 (can't remember).  Oddly enough my coral all looked fine because it was stable I guess.  The trend became that I would do a water change which would raise it 1dkh, and by the next water change (a week later, I upped my schedule to weekly from bi-weekly to try and keep up with demand) it would have dropped 1dkh.  It was clear that water changes wouldn't be enough to keep alk up so I ordered Seachem Reef Builder to begin dosing.  I measured consumption for a week and came back with 0.2dkh/day.  I raised my alk to 7, and planned to dose the 0.2dkh/day to maintain it.  Alk started dropping faster once it was at 7 though, so I started dosing more to make up for the new daily loss.  @stellablue suggested that I keep alk at 8-9 for my LPS, so I raised it to 9.

 

Now here's where it gets kind of weird.  It started dropping really fast.  Between doses I'm sometimes losing up to 1dkh.  I don't think that's from the corals, it's maybe 50% LPS (not even probably).  I just ordered a salifert Mg test kit and Kent Tech M (in case I need to dose) which should arrive next week.  In the meantime I'm letting alk fall a bit everyday because the higher I keep it the faster it drops and the swings are really pissing things off (like to death ).

 

Does this sound like a magnesium problem or something else?  I forgot to add that my calcium seems to stay stable at 425-435, although I haven't tested it in a week or two.  I can do that when I get home (out of town until Monday).  I wasn't dosing for calcium because it wasn't dropping, but it was brought to my attention by @teenyreef that I should be dosing for both, so when the alk thing is sorted out I'll see where my levels are at and figure out how to dose.

 

Thanks for the help

[MockandRoll]

I think you are on the right track with mag. That would be my first guess. Also what test kit are you using? If I get erratic results, I will check with another kit before making drastic changes. What is the cal levels of the water change water. Could also be percipitation if cal levels are higher in the water change water. 

 

Also alk dropping faster after the initial increase can happen. Uptake is regulated by the alk levels. Corals stop growing and go into survival mode when alk is low (6ish)

 

Another driver of alk is pH. Do you have drastic increases in pH when no one is in the house?

[fishfreak0114]

2 hours ago, MockandRoll said:

I think you are on the right track with mag. That would be my first guess. Also what test kit are you using? If I get erratic results, I will check with another kit before making drastic changes. What is the cal levels of the water change water. Could also be percipitation if cal levels are higher in the water change water. 

 

Also alk dropping faster after the initial increase can happen. Uptake is regulated by the alk levels. Corals stop growing and go into survival mode when alk is low (6ish)

 

Another driver of alk is pH. Do you have drastic increases in pH when no one is in the house?

I'm using Salifert. It has yielded consistent results until recently. Unfortunately I don't have another kit and I don't think there's anyone near me who can check it with theirs. 

 

I haven't checked the Ca levels of the water change water but I will next time. I've never noticed precipitation before though, and I've gone back to bi weekly water changes since I started dosing. The alk drops largely whether or not I've done a water change. 

 

The reason I don't think it's the corals is because it drops a seemingly different amount everyday, meaning I can't dose a set amount. 

 

I've never checked pH before, and I don't have a kit for it. I doubt it changes much when people are home though, there's only two of us and a cat and we often leave the windows open when we're home. 

 

Sorry I couldn't give more solid numbers.  

[MockandRoll]

3 hours ago, fishfreak0114 said:

I've never checked pH before, and I don't have a kit for it. I doubt it changes much when people are home though, there's only two of us and a cat and we often leave the windows open when we're home. 

 

Sorry I couldn't give more solid numbers.  

 

You would be surprised. 

[fishfreak0114]

As of this morning the tank's alk is 7.1 dkh, and calcium is at 370!  I think it has been precipitating out.  My Mg test kit and supplement are scheduled to arrive within the next two days.  I have discontinued dosing because it is causing more swings than necessary.  For now, I think the best thing is to let alk drop however it will because when it hits a certain point it will stop and be stable (likely 5).  It was suggested to do a few large water changes to try and reset the tank's parameters.  I regularly use RSCP, but I'm concerned that doing a large water change with that will cause a big harmful swing.  Should I pick up some reef crystals and use that instead?