alk drops like a stone but ca & mg remain high

[KurtS]

Hi all, I could use a bit of advice.

 

I've been having some issues with zoas not opening & rics being deflated for an extended period now but unfortunately have only been able to dedicate myself to getting to the bottom of this recently.

So with new test kits in hand I set our for testing.

Values for the tank on saturday (04/11) were

sg: 1.025

Ph: 7.8
dKH: 6
Ca: ~500

Mg: ~1600
This was 6 days after the last 25% WC

 

Mixed up a new batch of water on sunday (04/12) and did a 25% water change, parameters of the new mix were:

sg: 1.025

Ph: 7.9

dKH: 10
Ca: ~560
Mg: ~1540

I tested again today (04/13) and found my alk was again down to 6, while I had expected it to be at least 7 due to the 25% WC yesterday.
Parameters:

sg: 1.025

Ph: 7.9
dKH: 6
Ca: ~600
Mg: ~1600

 

The salt I use is Sera Marin Reef salt, which is advertised as having 10 dKH and has elevated Ca & MG levels so the salt mix seems to fall within the spec of the manufaturer. I've also been using this salt since I started the tank 10 or 11 months ago and it should have a Ph/Kh buffer in it. Should.

Do note that I give Ca & Mg as an approximation as I am not used to the new JBJ tests yet and they are one of those add drops until the color changes types, with 20+ drops each and I'm sure some were smaller than others and I don't know how much this affects the reading.
The Mg test is also combined with Ca and is a detract Ca result from Mg+Ca result type of test.

That said you can see Ca & Mg values remain high but alk immediately drops like a stone to 6 again, which I take is the value it bottoms out at.
This is what puzzles me as I was under the impression these 3 parameters are closely related yet I only see one dropping dramatically while the other 2 remain high.
Also I have no LPS or SPS, some zoas & 2 ric should not eat up alk so fast right?

I had hoped doing some more WC's might remedy this but seeing it bottom out again after a day is making me doubt.

 

Any input or thoughts would be appreciated

[Mojado]

My 40B consumes alk at slightly more than 0.5/day.

[Mariaface]

If your tank consumes about 1dKH (seriously, coralline can do this super quickly) a day, it wouldn't be a surprise that you found the level back at 6. Do you have a way to dose it? The tank may be stuck at 6 because that's as low as alk will go before the animals stop using it as much. My tank stalled at around 5.6dKH before I began dosing alk.

[metrokat]

I've not heard of JBJ test kits, the popular brands are Salifert and Red Sea.

Coralline algae consumes a huge amount of alk, if you have very purple rocks and a lof of them, this could explain the drop.

I don't understand how your calcium and magnesium is increasing though.

I haven't heard anybody using the salt brand you are, but it never hurts to mix it well. The portion you are scooping from may have more magnesium so mixing the bucket prior to making your water could help.

[KurtS]

Thanks for the replies all, I do happen to have a quite a bit of coraline and it grows rather well too. In fact it's been positively thriving while all the rest has been slowly declining in health lately.
I'll look into dosing options, probably will need to wait till the weekend before I can visit an LFS and actually get product.

As to the tests & salt, on this side of the pond the widely available brands are a little different than in the US, mostly shops carry the German stuff.

The Ca & Mg results I believe may be off slighly but that is probably human error, I'm not used to this brand and I admit not having quite the hang of the rather more involved Ca & Mg tests quite yet.

The Kh one is straightforward though and I know I didn't mess that up at least

[KurtS]

OK, so I found a store that has Seachem reef carbonate in stock and that ships so I should be able to get this before the weekend.

Now I've never dosed this before so if someone would be so kind as to tell me if my reasoning on this is correct I'd appreciate it.

Currently I'm at 6dKh and I want to hit a target of 10 dKh (same as my newly mixed salt)
Seachem's dosing calculater works in meq/l so I'm starting at 2.14meq/l and want to go to 3.57 meq/l (conversion done with this http://saltyzoo.com/SaltyCalcs/AlkConv.php )

Using the Seachem dosing calculater with the above converted values and considering a water volume in my tank of 4.7 US gallons it gives me 6.7ml to dose.
I believe this is the amount that take me from 6 to 10 dKh in one go, am I correct?

 

This is not what I want to do ofcourse, I want to increase slower so I figured 4 days of dosing to raise alk by 1dKh a day.
A quick conversion later and I get 1.7ml to raise dkh by 1

Now as my tank seems to consume 1dKh a day I would need to raise it by 2dKh a day to get the desired effect.
Being wary of doing one dose a day of 3.4ml or 2 dKh in one go I believe doing 2 doses a day of 1.7ml would be better.

If this is too fast I could go with 2.5ml doses daily, raising in total 1.5dKh which should, given alk consumption, result in a net raise of .5dKh a day.

 

Once the target value is reached in the tank just dose 1.7ml daily and test often to evaluate consumption.

Any comments or suggestions welcomed.

 

edit: I would ofcourse test daily during the raising and daily for 2 weeks after the target is reached. Then every other day for a few weeks and finally settling down on once a week to coincide with the regular maintence shedule.

[VW_TDI_02]

Instead of doing the conversions, try this calculator instead.

 

http://reef.diesyst.com/flashcalc/flashcalc.html