Low alk on new tank

[Mr31415]

I know there are a million threads on this and I have read many of them. However this is still curious to me.

I have a newly set up 90g tank, 30lb cured live rock from cycled tanks, 40lb dry rock, 80lb aragonite sand. System has been up for 1 week. I use Red Sea salt at 35 PSU. According to the salt, I should get Ca 430, Mg 1310, KH 8 at 35 PSU. Here are my tank parameters measured using salifert:

24.9C, pH 7.98, 6.7 dKH, Ca 420, Mg 1370.

pH is accurate - just calibrated both Neptune probe and my Hanna probes, they match.

Why is alkalinity so low when I have no coraline algae growth yet, and no corals?

It is winter in Canada so CO2 is probably causing low pH. But alkalinity? I am not dosing anything.

 

[reefing102]

I’m curious if it’s the salt. Have you tested your newly mixed salt to see if it’s measuring within proper range?

If it ends up being your salt, It may possible some of the salt contents settled during shipping/storage and may need to be remixed by rolling/shaking the bucket.

That’s all I can think of off the top of my head. Can’t say I’ve heard of any bad batches of Red Sea Salt

 

[griss]

I’m curious if it’s the salt. Have you tested your newly mixed salt to see if it’s measuring within proper range?

If it ends up being your salt, It may possible some of the salt contents settled during shipping/storage and may need to be remixed by rolling/shaking the bucket.

^This

 

[Mr31415]

I’m curious if it’s the salt. Have you tested your newly mixed salt to see if it’s measuring within proper range?

If it ends up being your salt, It may possible some of the salt contents settled during shipping/storage and may need to be remixed by rolling/shaking the bucket.

That’s all I can think of off the top of my head. Can’t say I’ve heard of any bad batches of Red Sea Salt

If this is the case, what is the fix for the tank? Dose alkalinity supplement?

 

[griss]

If this is the case, what is the fix for the tank? Dose alkalinity supplement?

If that is the case, first roll/ mix your salt, mix a new batch and see what your Alk is. But, essentially, yes, does Alk and/or Kalk.

I had been using Coralife salt for years (early/mid 90’s) with no issue. The last two bucket I got had different batch numbers and both were super low in Alk and high in Ca. It happens.

 

[Mr31415]

I just mixed a batch of 1 liter from salt from the top of the salt container without stirring the salt. Parms:

pH 8.45
Temp: 19.5
34.75 PSU
8.5 dKH

So the salt is fine. What would the cause then be for the low alkalinity in the tank?

 

[kharmaguru]

I just mixed a batch of 1 liter from salt from the top of the salt container without stirring the salt. Parms:

pH 8.45
Temp: 19.5
34.75 PSU
8.5 dKH

So the salt is fine. What would the cause then be for the low alkalinity in the tank?

A couple spitball ideas.

Possible causes could be a precipitation event in the tank (it could be hardening into the sand and you wouldn't necessarily notice it, it could also have happened if you dumped a load of salt into the tank all at once rather than adding slowly), or nitrates from the cured rock or other source are consuming the alkalinity.

 

[griss]

Since the tank has only been setup for 1 week, I'd give it another couple weeks doing a weekly 20% water change and see if that improves things.

 

[Mr31415]

A couple spitball ideas.

Possible causes could be a precipitation event in the tank (it could be hardening into the sand and you wouldn't necessarily notice it, it could also have happened if you dumped a load of salt into the tank all at once rather than adding slowly), or nitrates from the cured rock or other source are consuming the alkalinity.

I made 30gal of RO/DI 1ppm TDS water in a container, started a pump, and added 4.5kg of salt over the course of a minute by slowly pouring it in to avoid precipitation.

 

[Timfish]

FWIW, something like 90% of the dissolved inorganic carbon (DIC) in a reef system is in the form of HCO3 or bicarbonate. The ratios of CO2 to HCO3 to CaCO32 varies according to pH. Marine algae use enzymes to break apart HCO3 to utilize the carbon for photosynthesis. There's certainly other organisms that will use DIC also.

 

[Mr31415]

Would diatoms consume carbonates driving down alkalinity? I see they are starting to grow in the tank on the live rock...

 

[Timfish]

Any thing that photosyntesises needs carbon so yes they would.

 

[shred5]

I would test newly made saltwater it could be your salt. Start there.
If you test and it is still off it may be the salt or a bad test kit. So next try a different test kit or take to a LFS to test to eliminate the test kit as a point of error..
I have had some bad Salifert test kits that were wrong. I like how easy they are to use but I have had some bad ones. I always test my new kit to the older one and have two means of testing. I also use Hanna but I have had bad reagents with them once too.

If it is still off next test salinity levels if these are off it could throw everything off. Not sure how you are testing salinity. Some ways can be pretty unreliable. I prefer floating hydrometers for accuracy and really they should never be off.


If it turnes out it is not the salt or bad test kit it could be happening in the tank even though seems unlikely for such a new tank..

Also Corals and coralline are not the only thing using up Alk. Bacteria does as do other things.

Also precipitation could be happening for some reason.

 

[Mr31415]

I would test newly made saltwater it could be your salt. Start there.

I did - see an earlier post from me. It is not the salt.

 

[Timfish]

Other considerations include house environment and shifts in biological dissolution of carbonate substrates. Alkalinity of a system can be affected by poor ventilation with outside air. I've seen systems have issues when homeowners go on vacation or even if thier kids leave for an extended time. As systems mature microorganisms and biofilms will alter the sorbtion properties as well as dissolve the substrates (1) (2) they colonize and will be adding DIC to the system.

The takeaway is understand there's a lot going on that we can't quantify and always be testing and dosing if needed.

 

[Mr31415]

Yeah it is cold outside, -20C, so all windows and doors have been closed for months now. Only the ventilation from the furnace circulates air.

 

[Mr31415]

I measured my alkalinity to be 5.9dKH yesterday (using both a new Salifert test kit and a Hanna HI772). Both read 5.9dKH. pH was about 7.98. I dosed 32ml of Red Sea Alk B supplement to the sump. After an hour I measured an alkalinity of 7.1 dKH and pH went up to 8.2. Next day, 24 hours later, I re-measured and Salifert said 6.2dKH, the Hanna said 6.3dKH. So in a tank with no corraline algae growth like I said, and no corals, running almost 2 weeks - is this drop of 0.8dKH per day normal?

 

[reefing102]

That seems abnormal to me. Mine I think was dropping about 1dkh a week

 

[kharmaguru]

This article from RHF has lots of useful information:

https://reefkeeping.com/issues/2004-12/rhf/index.htm

 

[Timfish]

This will sound crazy with outside temps at -20° C. Try using a small air pump and lots of airline to use some outside air to aireate your system for a little bit to see what happens with your pH and alk. It sounds to me like your house might have high CO2 levels. If so that will definitely push down your alkalinity. Alternately you could get a CO2 meter to check your house.