where is my alkalinity going??

Jack_L · Apr 24, 2026

hi, my tank is about 5 months old now, uglies still around some. its 140gals of water. i do 10% weekly water change. i just have small frags, the tank looks empty really
the are two small SPS, a birdsnest and a sytlo, trumpets, several frags, couple small cononlies of 15 heads, but in total, i'd say about 1 softball size. also tiny zoa and 3 mushrooms.
i have some fish.
3 firefish gobies, 2 cardinal, 1 tang, 1 clown gobie, 1 watchman, 1 sleeper gobi ,2 clowns, 2 peppermint shrimp, 1 pistol shrimp, 2 emerald crabs and i guess about 100 snails, certith, astrea, nassarius, trochus,

my ALK has been dropping, it was down to like 6. i realized i wasnt' mixing salt strong enough, i fixed that. and i've added seachem reef builder to get it back up too, but being new to salt, wondering if this this normal. i've been testing it more and i can see a small drop every couples days. i'm guessing from what i'm seeing it would drop over a full point in a week. calcium is dropping a little too, like 10 points every couple days.

basically i was wondering if this is normal, i thought with this much water, and doing WC every week, i would not need to consider dosing until a year or more out if/when my corals were really growing. to date, i've only seen growth in the birdnest.

thanks

fishyjoes · Apr 24, 2026

It's common to have to dose to keep up with demand when you have a good amount of stony coral but it doesn't sound like that's the case in your situation (a rather large amount of water vs a rather small amount of coral).

What are you using to test your salinity, alkalinity, and calcium?
Are you testing regularly and recording the results?
Do you have a fresh water (RO/DI) auto top off?

If you aren't in the habit of testing regularly it's easy to make a testing error and not realize it (I once discovered I was in the habit of not making sure the plunger on my syringe was all the way to the bottom when drawing out test liquid - causing all kinds of weird results).

When you're trying to get a situation under control it's helpful to test frequently (every day or even several times a day) and track the readings over weeks to learn the trends.

Randy Holmes-Farley · Apr 24, 2026

I would not classify it as abnormal, and unless the sand is hardening (a sign of excess precipitation of calcium carbonate), I'd just pick and use a calcium and alk supplement scheme.

This might help you pick a better method than you are using. I use Tropic Marin All for Reef.

Pros and Cons of Alkalinity and Calcium Dosing Methods

Pros and Cons of Alkalinity and Calcium Dosing Methods How to decide which is best for you and your aquarium. By Randy Holmes-Farley Supplementing calcium and alkalinity is one of the most important chemistry requirements for most reef...

www.reef2reef.com

Jack_L · Apr 24, 2026

i use salifert, i test weekly after the w/c. i have been testing the ALK/MG/CA more as of late. daily when i added reef builder to get it back up. i also paid LFS to use aquaspin, and their numbers were in line w/ Salifert. LFS testing was what tipped me off to having low salinity. i've recalibrated by refractometer.

i've read that ugly stage can eat up ALK. but i read a lot of things.

i manually topoff with RO water as needed.

the trend i'm seeing is ALK is being consumed. about 0.25 a day

Jack_L · Apr 24, 2026

Randy Holmes-Farley said:
I would not classify it as abnormal, and unless the sand is hardening (a sign of excess precipitation of calcium carbonate), I'd just pick and use a calcium and alk supplement scheme.

This might help you pick a better method than you are using. I use Tropic Marin All for Reef.

Pros and Cons of Alkalinity and Calcium Dosing Methods

Pros and Cons of Alkalinity and Calcium Dosing Methods How to decide which is best for you and your aquarium. By Randy Holmes-Farley Supplementing calcium and alkalinity is one of the most important chemistry requirements for most reef...

www.reef2reef.com

my LFS didn't have AFR. i think that is what i'll use after i burn through what i bought. i had several shrimp die, including a cleaner, and they said the low ALK is likely the issue. so i wanted to do something. when i went back and looked over my notes the ALK was dropping, but i just overlooked it i guess. someone else told me they went from two part to AFR and it worked well for them couple years now.

Randy Holmes-Farley · Apr 24, 2026

An alk of 6 dKH is not going to cause death of shrimp. It’s pretty close to ocean levels.

Jack_L · Apr 24, 2026

well my other theory on the shrimp was that the wc was prompting a molt. my Mg had dropped to about 1170. I read that could cause a failed molt. that prompted me to test my new water, and that was very low on Mg, every w/c was dragging down my tank Mg, which i didn't realize either. i brought the tank Mg back up with seachem too. that takes a LOT of product to bring up Mg. reminded me why I stopped using seachem in FW, some of their stuff is oddly expensive. i THINK the issue with new water was i hadn't stirred up the salt, i just dump it from a bag into a bucket. read that settling of salt can occur. i put all the remain salt in the existing water(and added more RO as needed) and when i tested that, the MG came up some. mixing at low salinity i assume also exacerbated to Mg level too. the CA was a bit over 500, my test and store test, but i don't think that would kill shrimp, and i didn't have anything precipiate out. additionally i really i am guessing, could have been anything to kill them.

they suggested low ALK as that would allow pH swings, and said that inverts are more sensitive to that.

Randy Holmes-Farley · Apr 25, 2026

Jack_L said:
well my other theory on the shrimp was that the wc was prompting a molt. my Mg had dropped to about 1170. I read that could cause a failed molt. that prompted me to test my new water, and that was very low on Mg, every w/c was dragging down my tank Mg, which i didn't realize either. i brought the tank Mg back up with seachem too. that takes a LOT of product to bring up Mg. reminded me why I stopped using seachem in FW, some of their stuff is oddly expensive. i THINK the issue with new water was i hadn't stirred up the salt, i just dump it from a bag into a bucket. read that settling of salt can occur. i put all the remain salt in the existing water(and added more RO as needed) and when i tested that, the MG came up some. mixing at low salinity i assume also exacerbated to Mg level too. the CA was a bit over 500, my test and store test, but i don't think that would kill shrimp, and i didn't have anything precipiate out. additionally i really i am guessing, could have been anything to kill them.

they suggested low ALK as that would allow pH swings, and said that inverts are more sensitive to that.

I don't know about failed molt and magnesium (I'm skeptical, however), but most home magneisum test kits are too unreliable to be worth using,a nd if you have seen a significant drop, its either test error or a substantial salinity drop. It never gets consumed faster than about 1/10th of the calcium consumption rate.

The fact that lower alk contributes to a higher pH swing is real, but VERY small and not an issue. Folks with a high swing (from aeration not being complete) do not report apparent issues.

More on magnesium testing:

Just say NO to magnesium testing: RMM is born

OK, this thread has been many years in the making, and I'm posting it here since folks in the chem forum are probably already tired of all the threads relating to problematic magnesium testing. I'm going to propose a method, let's call it the Randy Magnesium Method, or RMM for short. All good...

www.reef2reef.com

Jack_L · Jun 29, 2026

wanted to circle back to this as your skeptical comment wasn't forgotten. i've used the whole container of seachem Mg in my 150gallon system, i did notice some increase, but time and W/C undo it. i do get consistent result from the salifert, but it takes a LOT of salts to move the needle. however after more reading, and viewing. Mg is just to keep Ca and carbonote in solution, i'm not seeing any precipitation (if that is in fact just a white dusting). and my pH had always tested stable. it still tests 1155. i plan to move to all for reef once i understand it more, but their packaging says get level right before using it. so i'm looking up your DIY Mg solutions.

i think looking back the issue was dinos. i've read they can consume alk too. i did have snotty/uglies for quite a while, but nothing drastic was happening, and i was trying to be patient an not change to much. then it got worse FAST. my P and N went to zero. notice the SPS bleaching, and started losing many snails and shrimp. i joined mack dino group and they helped ID some toxic dinos. if i had any doubt about their toxic nature. i don't now. mack group IDed them as prymnesium parvum, but i've now seen the other varieties too now that i know what to look for. at the beginning all that i saw from a glass scraping was a solid slide of wiggling dinos. i've boosted my P and N and dosing waterglass(for at least a month now), and now am getting diatoms (but still see dinos, the swimming variety mostly), and recently a good bit of various green hair algeas i assume as I boosted my P and N, and added some ocean figi rock(to help with biodiversity) that i expect introduced new stains. (i've not solved that yet)

anecdotal dino observations:
1. my arms would itch after being in the tank
2. the water smelled like rotten beach
3. most of the snails were unable to touch the rockscape, they would relese or flip on back. the nassarious snails would extend themselve out of the shell and frantically flip and roll away to a non dino spot.
4. the yellow tang was a grazing machine, but then he went down hill in this same timeframe. i didn't realize about the dinos at the time. my mind went to flukes based on syptoms, but other thread here folks didn't see any signs of it. further reading indicated that its consumption of the dinos could do it.

any way, long thread to circle back to say i think you're right and thanks for insights.