High dKH (and keeps rising). It's driving me crazy!

[Slidecf]

Hi guys,

I've been dealing with a high dKH issue for quite a while now, and it's driving me crazy. I've tried lowering it by doing 20–30% water changes, but what I can't understand is that after just a few hours or days, the dKH starts rising again. Salinity remains stable (or at least doesn't increase), and I'm not dosing anything that should raise alkalinity. I'm using mostly Aquaforest test kits. The only thing I'm currently dosing is Colombo PhosPlus because I previously had low phosphate while battling dinoflagellates. That issue has already been resolved. Here are my latest water parameters:

I also tested a fresh batch of saltwater immediately after mixing it, before adding it to the tank (Salt mix: Aquaforest Reef Salt - Batch code: 8223913):

• Salinity: 1.025 / dKH (Aquaforest): 6.4 / dKH (Red Sea): 5.0 / Calcium: 390 ppm / Magnesium: 1280 ppm

I spoke with the owner of my local fish store, and he suggested that I start dosing calcium and magnesium because, according to him, increasing those levels would lower dKH. That doesn't really make sense to me, especially since I had elevated dKH even when both calcium and magnesium were within the recommended range. That said, I am planning to start dosing calcium and magnesium because they're currently a bit low. For reference, here are some of my test results from last year:

My Setup:

• Tank Size: 40 Gallons / Running for 2 years now
• Aquascape: Marco Rocks + Zanzibar
• Salt: Aquaforest ReefSalt
• Light: AquaKnight V3 60W + Aqualumini Solarium Blue
• Skimmer: RedStarfish SQ90-Plus
• Fish: 2 Ocellaris / 1 Firefish / 1 Green Chromis
• 1 Coral Banded Shrimp / Some hermit crabs and turbos
• Corals: GSP / Zoanthus / Leather Umbrella - Right now no SPS or LPS

Any ideas on what might be causing this issue?

 

[Randy Holmes-Farley Verified Community Expert]

Are you using any Aquaforest rock? That has been an issue for some. What is Zanzibar rock?

A few things raise alk, but not usually this much.

Can you list anything you add to the tank?

It may be test error.

 

[Randy Holmes-Farley Verified Community Expert]

Don’t add calcium and magnesium to lower alk. That will require very high levels and will make a precipitation mess.

There are better ways to lower it if it actually is high, such as sodium bisulfate,,or a water change with zero alk seawater.

 

[Slidecf]

Are you using any Aquaforest rock? That has been an issue for some. What is Zanzibar rock?

A few things raise alk, but not usually this much.

Can you list anything you add to the tank?

It may be test error.

No Aquaforest Rock. I'm using only Marco Rocks and some Zanzibar rock. Zanzibar is a type of rock that's commonly sold here and is a bit cheaper per kilogram. I have two large pieces that serve as the base structure for the Marco Rocks. Oh and the substrate i'm using is Reeflowers PearlWhite. Here's a picture from the internet of what Zanzibar rock looks like:

I also considered the possibility of a testing error, which is why I started checking alkalinity with my Red Sea test kit as well. You can see some of the results in the image from my first post. The Red Sea kit consistently gives much lower dKH readings than the Aquaforest kit. In some cases, instead of showing an increase, it even shows a decrease in dKH. Since that didn't make any sense and the results were so different, I decided to have my local fish store test my water as well. Those results are shown on the third line of the table in my first post. (By the way, they also use an Aquaforest test kit.)

 

[Slidecf]

Don’t add calcium and magnesium to lower alk. That will require very high levels and will make a precipitation mess.

There are better ways to lower it if it actually is high, such as sodium bisulfate,,or a water change with zero alk seawater.

Thanks for the tip!

What really bothers me is that the dKH just keeps rising. Even if I were to do a water change with seawater that had zero alkalinity (or, more realistically, with my freshly mixed saltwater, which measures around 6.4 dKH), after a while the tank's dKH starts increasing again. To me, the real issue isn't simply lowering the dKH—it's figuring out why it keeps rising and how to keep it stable.

 

[Slidecf]

I think i should mention that i also used a littlebit of Aquaforest StoneFix cement on the aquascape (but this was 2 years ago)

 

[Randy Holmes-Farley Verified Community Expert]

I expect that one or both of those rock types is slowly dissolving in your system. Many folks have marco rock without that issue, so unless yours different somehow, or your demand is so low that it is not offsetting the rock dissolution, the Zanzibar seems a more likely culprit.

 

[Randy Holmes-Farley Verified Community Expert]

I think i should mention that i also used a littlebit of Aquaforest StoneFix cement on the aquascape (but this was 2 years ago)

How long have you had the alk issues?

Here's a thread on the Aquaforest issue:

https://www.reef2reef.com/threads/i...ing-aquaforest-man-made-rock-to-sump.1082013/@A_Blind_Reefer

 

[Slidecf]

I expect that one or both of those rock types is slowly dissolving in your system. Many folks have marco rock without that issue, so unless yours different somehow, or your demand is so low that it is not offsetting the rock dissolution, the Zanzibar seems a more likely culprit.

Hmm, should they still be dissolving two years after I added them? As I mentioned before, I also used some AF Stone Fix cement to bond parts of the aquascape together, so I'm wondering if that could be contributing to the issue.

I've actually been dealing with this for about a year and a half. At first, I was using Reeflowers Caledonia Coral Salt, and my Red Sea test kit always showed a very low dKH. I thought the salt mix might be the problem, so I switched to an Aquaforest test kit and Aquaforest Reef Salt instead. Here are the test results from when I first noticed this trend of dKH gradually increasing:

As I mentioned earlier, the Red Sea test kit consistently gives me readings that are about 2 or 3 dKH lower than the Aquaforest test kit.

I even considered removing the entire aquascape and doing a water change to see if the dKH would still keep rising. The only thing holding me back is that I'm worried it would stress the fish, since they wouldn't have anywhere to hide.

 

[Slidecf]

Aquaforest provides an ICP analysis for every batch of their salt. Here are the results for my batch:

 

[EricR]

The link noted in post# 8 is an interesting (long) read.
Beyond that, I'll just say that I:
- started seeing noticeable alkalinity rise with no dosing at about the 2 year mark in my soft coral tank
- fought it off for about 1 year by doing low alkalinity water changes using sodium bisulfate
- issue eventually subsided, I assume due to coral growth

 

[Randy Holmes-Farley Verified Community Expert]

Hmm, should they still be dissolving two years after I added them? As I mentioned before, I also used some AF Stone Fix cement to bond parts of the aquascape together, so I'm wondering if that could be contributing to the issue.

I've actually been dealing with this for about a year and a half. At first, I was using Reeflowers Caledonia Coral Salt, and my Red Sea test kit always showed a very low dKH. I thought the salt mix might be the problem, so I switched to an Aquaforest test kit and Aquaforest Reef Salt instead. Here are the test results from when I first noticed this trend of dKH gradually increasing:

As I mentioned earlier, the Red Sea test kit consistently gives me readings that are about 2 or 3 dKH lower than the Aquaforest test kit.

I even considered removing the entire aquascape and doing a water change to see if the dKH would still keep rising. The only thing holding me back is that I'm worried it would stress the fish, since they wouldn't have anywhere to hide.

Depends on what they are made of. Some rocks may dissolve until none is left.

 

[Randy Holmes-Farley Verified Community Expert]

The link noted in post# 8 is an interesting (long) read.
Beyond that, I'll just say that I:
- started seeing noticeable alkalinity rise with no dosing at about the 2 year mark in my soft coral tank
- fought it off for about 1 year by doing low alkalinity water changes using sodium bisulfate
- issue eventually subsided, I assume due to coral growth

When demand is very low, natural dissolution of rock and sand may outpace consumption.

 

[Slidecf]

Depends on what they are made of. Some rocks may dissolve until none is left.

Hmm, I see. That's good to know.

When demand is very low, natural dissolution of rock and sand may outpace consumption.

So, would it make sense to add a few SPS corals to increase alkalinity consumption? Should i buy some?
I've tried keeping some LPS corals, such as torches and frogspawns, but they slowly shrink until they eventually die. I still don't know what's causing it. It could be the lighting, flow, or lack of nutrients—I really can't tell. After losing a few of them, I became reluctant to spend more money on new corals just to watch them die again . I've never tried keeping SPS corals, though.

Zoanthids, GSP, and my leather toadstool all seem to be doing well. The GSP has grown a lot, and some of the zoanthids have spread quite a bit, while others have remained fairly stable. The leather umbrella is my newest addition. It seems stable so far—no noticeable growth yet, but it's not showing any signs of decline either.

 

[Randy Holmes-Farley Verified Community Expert]

I might try to get a handle on why corals die before adding more.

If I could not figure out where the alk is coming from (tap water can add it), I would use sodium bisulfate to reduce alk to zero in new salt water, aerate it well to blow off the CO2, and use it for regular water changes.

https://www.reef2reef.com/threads/s...in-new-salt-water-or-in-display-tanks.362825/

 

[A_Blind_Reefer]

How long have you had the alk issues?

Here's a thread on the Aquaforest issue:

https://www.reef2reef.com/threads/i...ing-aquaforest-man-made-rock-to-sump.1082013/@A_Blind_Reefer

Hard for me to follow as I don’t do pictures so I’m not getting the test results. Sounds like a lot of differing test result values between various test kits and lfs test, with some water changes thrown in as well. I’d be curious on test results by one single kit, with no changes, tracking over a period of time. Like testing freshly made up saltwater, leaving the freshly made up saltwater in its bin and testing again 24 hours later to compare. If alkalinity Is increasing at this step, I would think it’s a testing/kit error. Same with the tank water, test it and then test again 24 hours later with no changes (no water changes, no additives, no top off). Just so it’s apples to apples and looking for the trend. Also curious if ph/Co2 of source and/or tank could factor into this? I haven’t heard of issues with Marco rock and alkalinity, and googling z(s)ansibar rock, it sounds like it’s natural limestone from riverbeds and quarries. I’m curious to know if it is the rock dissolving.

 

[Slidecf]

Hard for me to follow as I don’t do pictures so I’m not getting the test results. Sounds like a lot of differing test result values between various test kits and lfs test, with some water changes thrown in as well. I’d be curious on test results by one single kit, with no changes, tracking over a period of time. Like testing freshly made up saltwater, leaving the freshly made up saltwater in its bin and testing again 24 hours later to compare. If alkalinity Is increasing at this step, I would think it’s a testing/kit error. Same with the tank water, test it and then test again 24 hours later with no changes (no water changes, no additives, no top off). Just so it’s apples to apples and looking for the trend. Also curious if ph/Co2 of source and/or tank could factor into this? I haven’t heard of issues with Marco rock and alkalinity, and googling z(s)ansibar rock, it sounds like it’s natural limestone from riverbeds and quarries. I’m curious to know if it is the rock dissolving.

Ok, i will try to do that and i will bring the results as soon as i have them.
Thanks for the help!

 

[Slidecf]

I'm still running a few more tests, and I'll post an update soon.
That said, I'm starting to strongly suspect that the Zanzibar rock is almost melting in my system. I'm pretty sure there's now a large hole where there used to be only a small gap when I first set up the tank. If that's really the case, it could explain why my dKH keeps rising so dramatically.

I'll wait for the test results first, but I think I'm going to remove the section of the aquascape that contains the Zanzibar rock, do a water change, and then see how the tank responds. Do you think that would be too disruptive or harmful to the tank?

 

[Slidecf]

Some updates:
I tested a freshly mixed batch of saltwater, and the dKH measured 7.8. After letting it mix for another 24 hours in a separate container, I tested it again and got 7.3 dKH. That makes me think there's something in my display tank that's causing the alkalinity to skyrocket. At this point, I strongly suspect the aquascape is the culprit.

I also bought Seachem Acid Buffer to prepare a near-zero-alkalinity batch of saltwater for a water change. I added enough to bring the alkalinity down to about 0.8 dKH. As expected, the pH dropped from 8.4 to below 5 (it's actually below the lowest value my test kit can measure, so I can't say exactly how low it is).

My question is: if I keep the water well-aerated, will the pH gradually rise again? If so, is it likely to return close to 8.4? And at what pH would it be safe to perform the water change, considering my display tank is currently at pH 8.2?
@Randy Holmes-Farley

 

[Randy Holmes-Farley Verified Community Expert]

Yes, the pH should rise as it blows off CO2, and I would do that.

Exact pH is not important, but if you can get it above 7, that would be good.