Lower pH of newly mixed salt?

[Saith]

Is there a way to lower pH in freshly mixed salt water and keep the alk where it is at? The threads I am finding with forum search are mostly saying it's a bad reading and the pH isn't that high. The rest seem to be about raising pH or lowering alk.

Something is up with my tank and I want to do a big water change. I mixed 100 gallons of fresh Tropic Marin Pro Reef and the alkalinity was 7.6dKH. My tanks is at 9.4dKH so I used Red Sea Foundation B alkalinity and bumped it up to 9.2dKk. But now the pH is 8.9. I would like to get it down closer to the tank's pH of 8.2. I'm assuming pH is more critical than alkalinity for a big water change.

Any advice is appreciated. Thanks.

Tank parameters:
Water Volume: ~155gallons (water in DT and sump)
Salinity: 34.9ppt (Hanna Pen)
Temp: 79.8°F (from Hanna salinity pen)
pH: 8.2 (Milwaukee Pen)
Alkalinity: 9.4dKH (Hanna)
Calcium: 440ppt (Hanna)
Phosphate: 0.03ppt (Hanna)
Nitrate: ~5ppt (Salifert test kit)
Ammonia: ~0ppt (Red Sea test kit)

Freshly mixed salt water:
Salinity: 35.0ppt
Temp: 81.1°F
pH: 8.9
Alkalinity: 9.2dKH

 

[Salty_Northerner]

Let it mix for a while is all I can suggest.

 

[Saith]

Okay, thanks for quick reply. Am I trying to aerate it?

 

[Salty_Northerner]

Okay, thanks for quick reply. Am I trying to aerate it?

Just keep a powerhead going.

Mayne you should've just left alk alone and dealt with it in the tank after it had time to mix with the other water? How much is in the aquarium for water now? You said you mixed up 100g and that's alot of water. Ahh nvm I see you said 150. So 50g to 100g I wouldn't stress to much.

 

[Salty_Northerner]

Ok I see you added alk so that's why your pH is up. I think once you start adding it to the tank the pH will start to drop. Is there a specific reason why you want your alkalinity so high?

Your tank will sort itself out with the pH.

 

[Saith]

Just keep a powerhead going.

Okay, thanks.

Mayne you should've just left alk alone and dealt with it in the tank after it had time to mix with the other water? How much is in the aquarium for water now? You said you mixed up 100g and that's alot of water. Ahh nvm I see you said 150. So 50g to 100g I wouldn't stress to much.

Ya, I should have just left it alone. This is the first time I've ever had to do a big water change. I was concerned mixing 90g of new salt water with 155g would drop the alkalinity by nearly 1dKH. I have generally tried to keep alk swings less the 0.5dKH per day.

I was watching a YouTuber the other weekend who was talking about big water changes and they said to adjust the mixed salt water's alkalinity with your tank before. They didn't mention anything about pH and it didn't cross my mind.

Is there a specific reason why you want your alkalinity so high?

I needed to start dosing alk and it settled in around 9dKH with the dose I was doing. I just left it there figuring that was a safe number. It would occasionally shift a little, but over a week it climbed up to 9.7dKH and it was slowly coming back down.

Going forward I'll make sure the tank stays near what my salt mixes up to. Lesson learned.

I think I'll do 50g change today, letting it mix with the 40g in the sump to bring the pH down a bit before getting pumped up into the tank.

Thanks again.

 

[Randy Holmes-Farley]

I suspect the pH is inaccurate (pH 8.9 in new mixed salt water is not normal to observe), but aeration alone will certainly lower it if it somehow is accurate and alk is less than 13 dKH.

 

[Saith]

I trust the reading. I just bought and calibrated the meter before testing. It matched my controllers pH reading on the tank at 8.2. After 6 hours of mixing it was up to 9.1.

I ended up only changing 25g and the tank went up from 8.3 to 8.4. This morning it was down to 8.2.

 

[Randy Holmes-Farley]

I trust the reading. I just bought and calibrated the meter before testing. It matched my controllers pH reading on the tank at 8.2. After 6 hours of mixing it was up to 9.1.

I ended up only changing 25g and the tank went up from 8.3 to 8.4. This morning it was down to 8.2.

Color me skeptical. But if you ever get pH too high in new salt water, aeration is the way to bring it down. At an alk of 8 dKH, pH will be 8.25 or less when fully aerated.

 

[Saith]

Color me skeptical. But if you ever get pH too high in new salt water, aeration is the way to bring it down. At an alk of 8 dKH, pH will be 8.25 or less when fully aerated.

First off, thank you for the replies.

I topped off the 105g container with another 25g of RODI and brought the salinity back up to 35ppt. The pH is now 8.7. Doesn't seem like it came down to much. Maybe I need more surface agitation.

What do you think could be the reason the Milwaukee pH pen would be high in the new salt water but correct in the tank? I suppose the tank could be way lower.

I added alk supplement to the new salt water to match the tank water, which was a bit on the high side apparently, at 9.4dKH. I thought up to 10dKH was fine, but sounds like I should keep it down around 8dKH.

 

[Saith]

Just remembered I have a Salifert pH test kit. I tested the water with that and it seems close to the pH pen.

New salt water is on the left, tank water is on the right.


Interestingly, the new salt water is down to 8.8dKH today (was at 9.4dKH yesterday). That should help bring the alk down a bit.

 

[Randy Holmes-Farley]

First off, thank you for the replies.

I topped off the 105g container with another 25g of RODI and brought the salinity back up to 35ppt. The pH is now 8.7. Doesn't seem like it came down to much. Maybe I need more surface agitation.

What do you think could be the reason the Milwaukee pH pen would be high in the new salt water but correct in the tank? I suppose the tank could be way lower.

I added alk supplement to the new salt water to match the tank water, which was a bit on the high side apparently, at 9.4dKH. I thought up to 10dKH was fine, but sounds like I should keep it down around 8dKH.

One can easily see if pH calibration is the issue by doing this aeration test. If the pH starts as 8.7 and does not drop a lot aerating with either indoor air or aoutisde air, the calibration is off. If it does drop a lot, then lack of aeration is the issue.


http://www.reefedition.com/ph-and-the-reef-aquarium/

The Aeration Test

Some of the possible causes of low pH listed above require an effort to diagnose. Problems 3 and 4 are quite common, and here is a way to distinguish them. Remove a cup of tank water and measure its pH. Then aerate it for an hour with an airstone using outside air. Its pH should rise if it is unusually low for the measured alkalinity (Figure 2). Then repeat the same experiment on a new cup of water using inside air. If its pH also rises, then the aquarium’s pH will rise simply with more aeration because it is only the aquarium that contains excess carbon dioxide. If the pH does not rise in the cup (or rises very little) when aerating with indoor air, then that air likely contains excess CO2, and more aeration with that same air will not solve the low pH problem (although aeration with fresher air should). Be careful implementing this test if the outside aeration test results in a large temperature change (more than 5°C or 10°F), because such changes alone impact pH measurements.

 

[Randy Holmes-Farley]

Just remembered I have a Salifert pH test kit. I tested the water with that and it seems close to the pH pen.

New salt water is on the left, tank water is on the right.


Interestingly, the new salt water is down to 8.8dKH today (was at 9.4dKH yesterday). That should help bring the alk down a bit.

i do not think alk of 9 dKH is any problem. i recommend 7-11 dKH.

Have you actually measured the alk in that new salt water?

 

[Saith]

Okay, seems like I need to do a better job with the aeration than just surface movement. I'll put an airstone in there.

i do not think alk of 9 dKH is any problem. i recommend 7-11 dKH.

Have you actually measured the alk in that new salt water?

Okay good. That is what I originally thought. After someone asked why my alk was so high, I did a search and read somewhere that 10 dKH in a low nutrient system can be a problem. I guess I can remove 9.7 dKH from the cause of my tank issue then.

Yes, I've been measuring alk in the new salt water along the way.
• 7.6 dKH after it was first mixed, close to the salt's spec
• 9.2 dKH after adding the alk supplement
• 8.8 dKH after topping up 25g

 

[Randy Holmes-Farley]

Okay, seems like I need to do a better job with the aeration than just surface movement. I'll put an airstone in there.



Okay good. That is what I originally thought. After someone asked why my alk was so high, I did a search and read somewhere that 10 dKH in a low nutrient system can be a problem. I guess I can remove 9.7 dKH from the cause of my tank issue then.

Yes, I've been measuring alk in the new salt water along the way.
• 7.6 dKH after it was first mixed, close to the salt's spec
• 9.2 dKH after adding the alk supplement
• 8.8 dKH after topping up 25g

Wait, you added an alk supplement to the new salt water? That is almost certainly what drive up the pH. I do not recommend carbonate for this purpose for this exact reason. Bicarbonate is the thing to use.

 

[Saith]

Wait, you added an alk supplement to the new salt water? That is almost certainly what drive up the pH. I do not recommend carbonate for this purpose for this exact reason. Bicarbonate is the thing to use.

Ya. I mentioned it a few time in this thread. haha

Good to know that I should have used bicarbonate. In the future I'll keep the tank alk close to what fresh salt water mixes to.

Thanks again for the help.