How is my DKH 9?

[hobbyreefer]

Tank is about 5 months old. I've only used Tropic Marine Pro Reef salt. BRS website shows the DKH for this salt is around 7. In the last 2 weeks it appears my DKH is slowing rising to around 9. I'm not dosing 2 part or anything else. I have a new 4 stage RODI unit for top off water and DKH in top off is showing 0. What could be causing the rise? I just have a few Acropora frags in the tank. In the last few weeks Coralline algae has exploded. I would think this would actually start to lower DKH. What is going on?

I'm testing with Hannah DKH digital tester. I also have a NYOS and SARA Alkalinity test kit. All 3 kits show ~9.

Salinity 35ppm
Phos ~.02-.05
Nitrate 5-10
Mag 1290
Calcium 420
Temp 77-79

 

[Flippers4pups]

Have you tested newly made saltwater?

 

[hobbyreefer]

Yes it was ~6.5 according to Hannah. I thought that was within the margin or error. Did a 20% water change this morning and the DKH still showing 8.9.

 

[Albertan22]

It’s likely your salt. Always test at least the first batch of water you make from a new pail of salt. Never trust that it will be the same as what is posted somewhere online, or even the same as your last pail. I always write the parameters I’ve actually tested it to be in sharpie on the side of the pail once I’ve tested it.

 

[hobbyreefer]

I did test my 30 gallon bucket of salt water before today's water change. DKH was under 7 in the new salt. I am dosing about 40 ML/day of neophos to keep phosphate detectable. I had a really bad Dino/Hair algae outbreak 5-6 weeks ago. During that time I was dosing microbacter7 and vibrant. I have not used any microbacter or vibrant in 3 weeks.

 

[C. Eymann]

What kind of rock did you start with? Added any lately? Do you have sand ? How thick? I know you said you are not dosing two part, but is anything else being added to the tank?
are you using a refractometer to measure salinity? Are you calibrating it with a 35ppt solution?

 

[hobbyreefer]

Yes calibrating refractometer to 35ppt using BRS solution. The tank started with 100 pounds real reef rock. I have not added any rock since the tank was started in November. The tank has about 1 inch of carib sea sand. Again, have not added anything since tank started. I turned my skimmer offline about a week ago since I'm battling 0 phosphates. The tank went fallow for ~50 days because of a velvet outbreak. I added a pentair UV sterilizer but I can't see that having an affect on DKH. I'm dump 1/2 teaspoon of reefRoids 2x daily to help add phosphate. Phosphates keep going to zero with heavy feeding, reefroids and neophos. Not sure if that is related to the DKH rising. I have a 160 gallon DT and ~20 gallon sump.

Thanks!

 

[C. Eymann]

Do you buy your salt by the bucket? do you shake /agitate your dry salt bucket or bag to compensate for settling?

otherwise, only other thing I can imagine is that the acids produced by bacterial processes (nitrifying and denitrifying) in the rock and sand in a newer system with very low demand may actually raise alk a bit.

If your rock is man made and wasn't acid cured/cooked it could be a possibile contributor too, possible bacterial acidification aside