High GH in Brackish Tank

[HancatAquariums]

I have a 55 gallon brackish tank I keep a GSP puffer in. The tank was set up almost three years ago originally for a figure eight puffer which unfortunately passed a few weeks ago. 

The tank sits at 1.010-1.012 salinity, temp 76-78, live rock, crushed coral substrate, an internal canister, a sponge filter, and an external aquaclear filter. Biweekly water changes 30-40%. 
 

Parameters: 8 ph, 0 ammonia, 0 nitrites, 0-5ppm nitrates. 900+ GH (according to my local shops automatic API tester).

My question is: why has my GH in this tank suddenly skyrocketed to extremely unsafe levels? 

I do not add any chemicals to this tank whatsoever, besides prime and marine salt. I’m completely flabbergasted as to what would cause this sudden increase (the crushed coral isn’t exactly new?) 

Any advice is helpful, I just want to figure this out for my puffers sake, thanks!

**I also want to mention the reason I use crushed coral and live rock is my tap sits around 6.2 ph, most of the puffers I keep prefer 7.8-8.2.

[face]

What’s the gh of your tap water after it’s been mixed with the salt and what salt are you using 

[Scapexghost]

Ppm or degrees?

[Tony s]

On 3/23/2024 at 9:01 PM, Scapexghost said:

Ppm or degrees?

dgH and dKh is relatively easy to convert. Mostly just divide by 20. Not quite but close enough in most cases. So the 900 would convert to 45 dGh roughly. Which, holy cra@@, is beyond liquid rock. 

So what exactly are you adding to get the tank in it’s brackish condition?

[HancatAquariums]

On 3/23/2024 at 9:18 PM, Tony s said:

dgH and dKh is relatively easy to convert. Mostly just divide by 20. Not quite but close enough in most cases. So the 900 would convert to 45 dGh roughly. Which, holy cra@@, is beyond liquid rock. 

So what exactly are you adding to get the tank in it’s brackish condition?

I use Red Sea marine salt, and seachem prime. I fill my bucket with tap, dose prime, then use a refractometer to dose the marine salt to 1.010-1.012 salinity. Other than that, I don’t have anything additional in my filters besides basic matrix and filter floss.

**I’m attaching a pic of the tank for better visualization. **

Live rock, driftwood, crushed coral substrate, fake plants (little to nothing plant wise survives in this salinity).

Edited March 24 by HancatAquariums

[face]

You said it suddenly went up what was it before? 
 

if my math is right (and it’s completely possible it’s off lol) you should get a gh of roughly 600 plus whatever is in your tap water since you basically going to get 40%of whatever the bucket says you’ll get at 1.030

[Tony s]

Maybe you’re having the same issue I was having. When I started using ro water, I was filling my tank with remineralized water every time. Using Seachem equilibrium. Not realizing that it doesn’t evaporate. Every time I topped off the tank. I was raising th gh I eventually got into the 20’s accidentally. 
 

maybe you’re having my issues except by using salt. The salt and additives don’t evaporate. Maybe just top off with regular water and then do a water change with the brackish water. That way the tank salinity, and hopefully the gh stays balanced 

just out of curiosity, has the tank salinity been increasing over time? You say gh has but how about the salt 

Edited March 24 by Tony s

[HancatAquariums]

On 3/24/2024 at 1:15 AM, Tony s said:

Maybe you’re having the same issue I was having. When I started using ro water, I was filling my tank with remineralized water every time. Using Seachem equilibrium. Not realizing that it doesn’t evaporate. Every time I topped off the tank. I was raising th gh I eventually got into the 20’s accidentally. 
 

maybe you’re having my issues except by using salt. The salt and additives don’t evaporate. Maybe just top off with regular water and then do a water change with the brackish water. That way the tank salinity, and hopefully the gh stays balanced 

just out of curiosity, has the tank salinity been increasing over time? You say gh has but how about the salt 

The salinity has remained at 1.011 for the last two weeks, I keep a lid on it to help with evaporation, so thankfully with it being such a high volume of water the salinity doesn’t fluctuate as much. However, my GH for this tank is usually 8-12. 
 

The only thing I’ve changed that I can think of was I added a new bag of crushed coral (20lb) roughly ~3 weeks ago. However, if my water is pretty alkaline, I’m struggling to understand how it would continue to buffer so heavily that my GH reached such an extreme ppm. (I’ve also done this in the past with no spike in GH)

[Tony s]

Extreme batch of coral? Fine powder in it?  Or possibly bad test? Doesn’t make sense. The rapid change to enormous gh

[HancatAquariums]

On 3/24/2024 at 1:04 PM, Tony s said:

Extreme batch of coral? Fine powder in it?  Or possibly bad test? Doesn’t make sense. The rapid change to enormous gh

That’s what I’m thinking as well, it just seems off. Of course it’s still my fault for not being more on top of checking my GH, however, I wish I could pinpoint the issue more clearly so I can ensure not to make it again. I appreciate your help tremendously!