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Reef Geek
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Discussion Starter · #1 ·
Guys,

Do you add anything to your RODI water to raise the pH before adding your salt mix? I am having a problem when I do water changes. My pH drops to 8.00 for several days as the kalk slowly brings it back up to 8.25. My corals and fish aren't too happy when this happens.

Help...
 

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I add Kent Reef Buffer to the tank when I do a water change. I think the directions have me add 1 tsp per 5 gallons water change. But don't add it to the salt mix, it will precipitate out. You have to add it to some fresh water and add it to the tank right after adding the new salt water. RODI water really needs it since the RODI treatment removes most of the buffering capacity of the water.
 

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What salt are you using? Some of the salt mixes vary a good bit in their alkalinity. Also, do you aerate the freshly mixed saltwater before doing your water changes? If you've got a lot of dissolved CO2 in the new saltwater when you add it to your system, that will drop your pH.
 

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Discussion Starter · #4 ·
Stanfill, thats what I have been doing after the pH has been at 8.0 - 8.1 for 3-4 days. Maybe I should start doing that at the water change.

Phantom, I am using IO Salt. I don't aerate the mixed salt water. Do you think that will help considering the drop takes 3-4 days to overcome?
 

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Little fish in a big pond
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It's a good idea to aerate new salt water. I'm lazy (as most people are!) so I use a pump or powerhead to do the mixing for me. Helps to dissolve all the salt too.

It's a good idea to do this the night before a water change if possible, but most mixes nowadays can be used "right away".... some say new salt water is caustic - that may be so if it's not aerated properly. I've had no problems using newly mixed water, but I'm using a Mag 5 pump in a 5 gallon bucket (and a 32 gallon trash can) to do the mixing, so it's getting pushed around very fast.

Have not had any problems with this method.

BTW a drop to 8.0 from 8.25 shouldn't be that big of a deal. Many tanks fluctuate that much in a day. Not that a swing is a "good" thing, but I'm thinking that might not be the problem, per se. I'd be considering the drop in dissolved oxygen instead - IMO that's why things aren't too happy.

Jenn
 

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Yeah, I would aerate your new saltwater for 24 hours if I were you. Jenn makes a good point about the oxygen. As I recall, some RO/DI units are so efficient they can remove dissolved oxygen from the water. If CO2 is a problem, hopefully aeration should help that too. Instant Ocean is actually pretty good on alkalinity, so thats probably not the problem.

If that doesn't help, then I guess I'm at a loss, as I've exhausted my limited knowledge. Maybe Tom or someone else can help.
 

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Discussion Starter · #7 ·
Jenn,

The DO change might be the ticket. Now that you mention it, with the reduced pH, I see fewer micro-bubbles forming on the surfaces of the items in the tank near the end of the photo period. Will aerating the mix help that much with the DO? If aerating the new water for 24hrs before adding to my system would help, why wouldn't my pH bounce back after the water was being aerated by my system for 24hrs? (BTW, I run a skimmer and still run my return over a drip plate over what used to be bio balls making bio-ball-falls :) )

Phantom,

I think you are right about IO Alk. I test parms every Saturday morning and my Alk was fine the Saturday after a Friday water change. I added a 1/2 dose of buffer last night to try and boost the pH a little. It hit 8.13 last night before the lights went out. Still below the 8.25 it normally hits.
 

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the problem is allowing for the time for the buffer system to stabilize. Freshly made Ro/DI is stripped of many items, and although it has a reduced O2, that really does not affect pH in the end solution. CO2 is everything in the control of pH for aquarium water for marine apps. Mixing the ASW 24 hrs prior to use allows for full stabilization of the buffer system and e
 

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The problem is allowing for the time for the buffer system to stabilize. Freshly made RO/DI is stripped of many items, and although it has a reduced O2, that really does not affect pH in the end solution. CO2 is everything in the control of pH for aquarium water for marine apps and it has a major effect of the equilibrium of the bicarbonate/carbonate buffer system. Mixing the ASW 24 hrs prior to use allows for full stabilization of the buffer system and equilibrium to occur between atmospheric CO2 and the pCO2 of the water column. Aeration helps with this and improves O2sat for the fishes, etc. as well. The use of mixing pumps helps a lot, as does the use of plastic "propeller" mixers for large batch apps, but the pH will not stabilize until the pCO2 reaches saturation and the buffers are allowed to reach equilibrium as well.

The upshot of this is that it is prolly not of significance for MOST applications, although sudden pH swings will have their effect on pH sensitive corals and other creatures (for example, clams in particular). To be on the safe side, mix your ASW 24 hours prior to the actual water change event.

HTH
 
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