Tank pH at night is 7.49 and nothing makes sense, I guess 7.5 is perfectly healthy for a reef?

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2Wheelsonly

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My tank hits 8.02 during the day, 7.49 at night. I have tried isolating my probes, putting them in different areas of the sump and tank and all readings are consistent. I have a very large skimmer with a line run outside.

Indoor co2 meter shows 688 on one (smaller unit) and a nicer larger unit shows 691... from my understanding these are healthy levels.

My tank's pH was usually 7.61 at night and 8.1 day but the fact that it's been dropping over time has me worried. I do not like negative trends without explanation. I decided to look at the most unreliable equipment in my tank and all signs always point to Neptune stuff. I threw away my probes, bought brand new lab grade apex probes (2) and re-calibrated them with brand new solution. Both probes are within .01 of each other so I am confident they calibrated correctly. When I place them in the solution packets they are 6.9 (7.0) and 9.9 (10.0).

Now, I have two things in my system that lower pH. One is a calcium reactor, a rather large one as my sps load is very high. The tank is 350G volume, lots of SPS colonies and 6 tangs, 2 wrasse, 2 clowns tanks dem: 96x30x24. The reactor is a GEOCR818 with two gallons of ARM extra course. My melting point is lower and pH measured leaving the reactor is 6.4. It barely keeps up at 90ml per min drip (kamoer).

I feel the reactor is dialed in, I set it up with an initial effluent flow rate of 60ml/min and 1 bubble per 6 seconds. Measured effluent DKH at 15, then moved up to 5 bubbles and 65/ml and then eventually getting to micro adjustments to where my DKH was 20 and my bubble rate is 1 bubble per 3.2ish seconds and drip rate is 90. The controller is there to turn off regulator for emergencies but that never happens as it runs 24/7.

Alk is 8.5
Temps 77.8-78.1 consistent

My other piece of equipment is a large sulfur denitrator I used to keep no2 at 2ish. I do not carbon dose. The effluent drips into a DIY aeration chamber with a large air stone. The air pump has an inlet that allows me to pull air directly from outside and it's a powerful air pump. I also have a second airstone in my sump intake chamber just to bring air in. So, that makes 3 different areas I am bringing air in the sump. I know the air stone works because my effluent out of the aeration chamber is 8.2 day and 7.9 night consistent.

I tried the air test:

Indoor test at night: 7.9
Outdoor test at night 8.1

Indoor test day: 8.2
Outdoor test day: 8.4

New salt water in my mixing station stays consistent with above at 8.2 day/7.9 night (in same room as tank).

Why and how can my in tank pH be so freaking low? 7.49 and still dropping slowly over time. At what point does it stop? Nothing is adding up, what in the world of science is happening inside my tank to cause my pH to drop? Fish seems fine? Shrimp/snails seem fine? Acros seem fine? Have I unlocked a new breakthrough in low pH tank health!?! Can I save the great barrier reef?!

Also, my salifert (yuck) pH kit is consistent with my probes also.
 
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GlassMunky

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I think you’re overthinking it. You’re corals and fish are fine so there no reason to do anything. Don’t chase numbers just to have the “perfect number”.
Also, when I ran a CARX That’s about where my Ph stayed also so I’d say it’s still normal.
 

D4jack

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Also what are your co2 readings in the summer? That is a good baseline to compare with. Co2 is usually much higher indoors in the winter. If you live in a cold area. I'm in Ohio and it definitely gets cold here.
 
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Also what are your co2 readings in the summer? That is a good baseline to compare with. Co2 is usually much higher indoors in the winter. If you live in a cold area. I'm in Ohio and it definitely gets cold here.

my house has been the opposite so far in the 5 years I lived here. My windows stay shut year round but it’s an older home that’s not super sealed up. The ac/heat unit is an all electric heat pump that constantly runs summer/winter. My indoor co2 levels in summer run twice has high as in winter. Nobody has been able to explain why...
 
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josephxsxn

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Your skimmer isn't providing perfect gas exchange, so your seeing peaks when the photoperiod is on with co2 going down being consumed and drops when its off while co2 buildup is increasing. If you had perfect gas exchange the PH would remain pegged to your room's co2. My drop isnt as bad at night but I still can see 7.9 to 8.3 every day, it was a smaller range when I ran macro alage on a reverse photo period but stopped that a while back for other reasons. I also run an outdoor skimmer line.

8.1 PH values with DKH 8.5 and CO2 ~650 makes sense based on the Co2SYS Tables here. The only thing that could be changing is the co2 levels inside the tank which cause this swing. That is because PH is made up of co2 + alk (as you can see in the co2 tables.) But the 7.6 PH means your CO2 levels (assuming DKH is pegged) is hitting 2500ppm somehow at night and 600-700 during the day.

I dont use a calcium reactor so cant help you there for how it would impact these 2 variables. Maybe turn it off for a night?

 
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josephxsxn

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Oh as for your summer vs winter problem. I am guessing your AC unit has no exhaust while your furnace does. Running the furnace exports gas from the house, AC loops it back. On my furnace I have a bypass for summer to make it a closed loop.
 

Randy Holmes-Farley

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I strongly urge you to increase the aquarium aeration. The aquarium is clearly inadequately aerated.

True pH 7.4 will greatly stress calcifying organisms, allow coral skeletons to slowly dissolve, and slowly dissolve aragonite rock and sand.
 

DucatiGtr

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I don’t want to jinx myself here..
I have nvwe in my life since the year 2000 ever tested ph in any of my systems..
I have multiple tanks and my main display has a ton or coral, high end pieces as well.
These threads make me nervous..
But has anyone actually had ph issues where it actually affected coral?
 
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Oh as for your summer vs winter problem. I am guessing your AC unit has no exhaust while your furnace does. Running the furnace exports gas from the house, AC loops it back. On my furnace I have a bypass for summer to make it a closed loop.
I thought heat pumps work almost similar in winter vs summer as they take heat/cold out of the air and in winter supplements with electric coil heat when it’s really cold out and heat pump can’t keep up.
 
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I strongly urge you to increase the aquarium aeration. The aquarium is clearly inadequately aerated.

True pH 7.4 will greatly stress calcifying organisms, allow coral skeletons to slowly dissolve, and slowly dissolve aragonite rock and sand.
I can’t figure out a better way to aerate than I already am? I have two large gyres on each basically aimed at surface. My surface agitation is chaotic to the point I have salt creep on my lights 14 inches off the water.
 

josephxsxn

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I can’t figure out a better way to aerate than I already am? I have two large gyres on each basically aimed at surface. My surface agitation is chaotic to the point I have salt creep on my lights 14 inches off the water.

What kinda skimmer do you have? How long is the tube to get to the outdoor airsource?
 
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What kinda skimmer do you have? How long is the tube to get to the outdoor airsource?
Summer is generally mid May to September, air line outside is a 1 in pvc pipe 20ft in length drilled through wall to the outside. Could this be an organics issue inside the tank?

skimmer is a life reef 36 inch rated for 400-600g Upgraded Venturi
 

Randy Holmes-Farley

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Maybe your tank pH is not what you think.

What was the "starting" pH of the aeration tests you did? Was it measured away from the tank?

pH measurement interference near the tank is a common issue.
 
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Maybe your tank pH is not what you think.

What was the "starting" pH of the aeration tests you did? Was it measured away from the tank?

pH measurement interference near the tank is a common issue.

doing it just now as we speak, pH is up a bit as the lights are on. Currently tank probe says 7.67, filled 4 cup measuring cup with tank water. Placed pH probe in it right next to sump on my step ladder. Reads 7.68 after 2 mins settle.

placed air stone in it, after 4 mins it’s at 7.99. Measuring cup is in the same place (ladder next to sump). Took air stone out let sit for 10 mins and pH is holding at 7.9 with still water in cup as I type this.
 
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josephxsxn

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placed air stone in it, after 4 mins it’s not at 7.99. Measuring cup is in the same place (ladder next to sump). Took air stone out let sit for 10 mins and pH is holding at 7.9 with still water in cup as I type this.

This is with the cup indoors correct and air source is indoors? (I know you said next to sump, just confirming)
 
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This is with the cup indoors correct and air source is indoors? (I know you said next to sump, just confirming)
correct, I have a second air pump running in the room not attached to the outside line. Also want to note that I always keep around 60G of mixed saltwater ready to go in my mixing station. There is no pump in it and water just sits until I aerate right before I need to use it. It never drops below 7.85 at night and is in the same room as my tank.

note: freshly mixed salt water is instant ocean with alk around 9.8-10
 
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I ordered a secondary chamber that I will fill with crushed coral. I can’t think dripping 90ml per minute of pH 6.4 water directly from my calcium reactor is helping things.
 
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