Help - Cant keep up with the alkalinity

Every tank is different, learning the needs and balance of each set up is a challenge. My current conditions are no different. This set up is challlenging to say the least.
I can’t keep up with the alkalinity needs of this set up and it is driving me nuts. I can’t seem to get the alkalinity to rise above 6.7-7.0 no matter how much I am dosing. If If I dose more it takes more and eventually falls back to that 6.8-7.0 Mark.
Phosphate is typically .04
Nitrates are very low typically undetectable to about .25
My magnesium is staying high @ ~1350
My calcium is staying around 420-450
I have historically kept my alkalinity around 8-8.5, but can’t manage to get above 7 and it’s got me worried about long term effects of stony corals.

I have more coralline algae in this tank than any set up I’ve had in the past and Im wondering if it is just being such a hog that I haven’t found the sweet spot yet. It doesn’t seem right though because My Calcium needs don’t seem to be increasing as the Alk is. They should stay at a similar need as my experience has been over the years.

I have read that nitrate levels can have an effect on alkalinity needs but I don’t understand how that jives.
The system has a total water volume of about 150 gallons, I have Chaeto in my sump, run a protein skimmer, and do a 10 gallon water change almost every weekend.
Lighting is 8 bulb T-5
Plenty of fish, snails, hermits, shrimps and crabs
The only nuisance algae I have is this red filimentaceous stuff that looks like red velvet (nothing I have found will eat it)
I’m looking for any suggestions, explanations, or insight based on experience that might help me figure this out.
Please let me know your thoughts as I am one parameter away from figuring this tank out.

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That’s super weird. How are you supplementing your alkalinity?

I’m sure I’ll be of no help at all. Maybe?
I have not graduated to your level yet. What I have learned is that every aquarium finds its own balance over time. While we are making changes and chasing numbers, we neglect that period of pure observation. An aquarium has an amazing immune structure which will weaken over time if not allowed to be used on its own. Kinda like muscles in the body. I do have the advantage of being able to spend hours per day just quietly conversing and feeling and receiving vibes from my tiny oasys. It’s a total living thing and will react to your vibes.

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I use baking soda, I posted on another reef related forum and received some good feedback

I may be just a little gunshy and over thinking this whole thing.

I am going to increase my dosing amount until I see the results I need over the next couple weeks

This tank has a higher demand to start with plus I think I was screwing up the math for what I need.

I really was not being nearly aggressive enough with the amount of carbonate being added

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Thanks, I think there is definately something to be said about letting a tank work itself out in certain aspects. I think people often react too quickly to nutrient issues, the bio load will generally balance itself out if changes are gradual. Quick fixes in a bottle have never ended up well for me.
In this particular case I think I have taken gradual to the extreme and just not getting the results because the need for Alk exceeds the supplementing i have been doing

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Similar comment to @WaterOasis — you’re at a much more advanced level then me @Donavon — but I think you’re going down the right path. One thing I have learned is to keep a good log and make slow changes. I’d write down a sensible plan to slowly up the dosage, regularly test, and suspect you’ll find the right equilibrium.


Hmmm… well keep us posted!

I was thinking maybe it was precipitating out, but maybe it is a dosing amount issue. :man_shrugging:

what is your PH doing? personally i have found that to be the #1 parameter to keep an eye on.
do you dose Kalkwater in your top off? if not, i would start, but only if you are monitoring your PH.

I don’t really monitor PH, but I think I will start tracking it. I don’t think PH will affect the stability of alkalinity but could be wrong.
I used to top off with kalk water but it didn’t keep up with my Alk needs in the past. My system is roughly 160 gallons and top off fluctuates but is typically around one gallon per day. When I took kalk out of my routine in the past PH was not affected in a noticeable way. I think it would be one more thing to worry about in the sense of keeping alkalinity stable.
I did increase my dose with bicarbonate over the past couple days. It seems to be steady second day in. I’ll see tonight when I get home where I am day 3
If I am still steady, i will know that my daily need is being met, then I will add by hand, additional each day to get to 8.5.

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when I clean off my coraline algae I see about a .1 dkh difference in uptake- per day! So it can make a big difference.

I like to run mag at 1350 - 1450

Make sure you are testing at the same time each day - like testing before your photo period will yield a much higher result than after the photo period

check test kits - i like hanna, but old reagent can throw it off

calibrate your dosing pumps


I’ve had similar problems in the past and the recommendation would be to do two 80% water changes and and that you should be back to where you wanna be. Sometimes the ionic balance just gets in a certain way. It’s all chemistry. The extra carbonate precipitates out and doesn’t stay in ionic form in the water. It’s really not a big deal big deal either way but if you want to go and reset the chemistry do two 80% water changes one week apart.


Are you still using the same salt mix that you used before?

Please let us know what is your daily PH reading. And if possible , what is your nightly PH swing.

My ph has been 7.8-8 I usually test at night between 6-10:00

I haven’t dug in too deep to see what day vs night is

I really think I was just not dosing a high enough amount. I was hand dosing to get up to the 7dkh Mark then adjusting the automatic doser to what I thought it was consuming (not taking into consideration the bit that I hand dosed)
I kept coming up short each day not making the mark
So I quit dosing by hand. Then I doubled my dosing hours from every two hours to every hour. This got me up to seven consistently for a couple days
I then raise my dose by 10 mil each hour. I have seen it gradually climb about 1/4-1/2dkh each day
I am sitting at 8 1/4-8.5 today

If I reach 9 in the next couple days I will drop my dose by 5 mil.

I getting close to dialing it in

Thanks for everyone’s comments and help!!


Same salt, reef crystals

Sounds like you have a handle on it. If you run into issues just post again or send me a private message. I could write a book on this topic.
Just keep increasing your dosage. Do keep in mind that in the long run, if you stick with bicarbonate, your sodium level will start to increase, especially if you are not doing significant regular water changes.

Your Alkalinity level is the bio-limiting factor. Calcium will not continue to decrease once Alk gets a bit below 7dKH. Much of the ocean is 7dKH and with many parameters it is wise to pay attention to natural reefs. That said higher levels usually do not cause issues, but lower levels will. I usually target 8-9dkH.

I have heard people say, “My tank likes to be below 7dKH and naturally goes there”. It is not the case. Your system just needs more carbonates added.

Your coralline algae is absolutely responsible for sucking out carbonates. Carbonates were the main component of the old school product, “purple up”. FOWLR tanks with a significant amount of coralline algae can quickly get low in Alk and as a result pH swings.

I personally LOVE using Kalkwasser to start with. It usually does not keep up with demand, but it is very economical and helps get some stability.

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I forgot to ask what test kits / equipment are you using and when do the reagents expire? Always wise to make sure numbers make sense and testing is sound before chasing numbers too far.

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I use:

Red Sea to test nitrates/phosphates

Salifert to test magnesium and alkalinity

And use API to test calcium

All test kits were recently purchased and expirations are late 2022