Phosphate, PH and Aragonite

[PaulB777]

My 150g very lightly stocked tank (6 fish and few inverts) is a little over a year old and has never really thrived. While most of the parameters have been fine (Temp: 80, Salinity: 35, Alk: 8.5, Cal: 480, Mag: 1510) I've historically struggled with my pH, Nitrates & Phosphates, and predictably I have had algae issues due to the nitrate & phosphate problem. I dosed NoPox for a number of months which did help with the nitrates---those are currently around 10---however, it really didn't seem to affect my phosphate levels, which never seem to be able to get below .1 on my Hanna ULR checker and left unchecked will approach .25 or more. I also run 2 BRS media reactors (one with GFO and one with RowaPhos) which don't seem to do a thing. I also do twice a month 15% water changes.

The only thing that has ever had an effect on my phosphate levels is Phosphate-e (lanthanum chloride) which does seem to work...but only for a very short time. For example, yesterday morning, my phosphate level was .17 so I dosed around 70ml of Phosphate-e. In the evening, my phosphate level was .11, however, by this morning it was back up to .19. So I just never seem to get ahead of it. Note also that I feed BRS pellets very lightly with an auto-feeder so I don't really think that's the source of the problem and my tank and ATS are sourced from a BRS RO system. I know that others have reportedly run great tanks with higher phosphate levels, however, I have significant algae levels which I strongly suspect are related to this so I'd like to address it.

I've heard that phosphate can "leach out of rocks" which could be a source. One thing that I'm wondering though based on some research here is the relationship between pH, phosphate and the Aragonite base (~1.5") that I have in my tank. My pH has pretty consistently been low (around 7.7) which I've never "chased", however, I've heard that a lower pH like that can leach out phosphate somehow from Aragonite? Could that possibly be my problem? If so, what would you guys recommend as a fix?

 

[Randy Holmes-Farley]

My 150g very lightly stocked tank (6 fish and few inverts) is a little over a year old and has never really thrived. While most of the parameters have been fine (Temp: 80, Salinity: 35, Alk: 8.5, Cal: 480, Mag: 1510) I've historically struggled with my pH, Nitrates & Phosphates, and predictably I have had algae issues due to the nitrate & phosphate problem. I dosed NoPox for a number of months which did help with the nitrates---those are currently around 10---however, it really didn't seem to affect my phosphate levels, which never seem to be able to get below .1 on my Hanna ULR checker and left unchecked will approach .25 or more. I also run 2 BRS media reactors (one with GFO and one with RowaPhos) which don't seem to do a thing. I also do twice a month 15% water changes.

The only thing that has ever had an effect on my phosphate levels is Phosphate-e (lanthanum chloride) which does seem to work...but only for a very short time. For example, yesterday morning, my phosphate level was .17 so I dosed around 70ml of Phosphate-e. In the evening, my phosphate level was .11, however, by this morning it was back up to .19. So I just never seem to get ahead of it. Note also that I feed BRS pellets very lightly with an auto-feeder so I don't really think that's the source of the problem and my tank and ATS are sourced from a BRS RO system. I know that others have reportedly run great tanks with higher phosphate levels, however, I have significant algae levels which I strongly suspect are related to this so I'd like to address it.

I've heard that phosphate can "leach out of rocks" which could be a source. One thing that I'm wondering though based on some research here is the relationship between pH, phosphate and the Aragonite base (~1.5") that I have in my tank. My pH has pretty consistently been low (around 7.7) which I've never "chased", however, I've heard that a lower pH like that can leach out phosphate somehow from Aragonite? Could that possibly be my problem? If so, what would you guys recommend as a fix?

The pH effect on binding is quite minor, but any bare calcium carbonate surface can bind a huge amount of phosphate is the levels in the water were previously high. Many ppm worth.

There's a limited amount present, so if that is the source, just keep reducing it, and the lanthanum is an OK way to do it.

 

[Randy Holmes-Farley]

Since you asked about it, here's a graph of the pH dependence of the binding of phosphate to aragonite:

Phosphate Study in Florida Bay

 

[mdb_talon]

I love this forum. Learn a heck of a lot more science than I ever did in class.... and actually enjoy it.

 

[GotCrabs]

Hey PaulB777,

I've been on a reading frenzy in recent months. I've taken apart my 150g system and restarted after about 9 years. Here are some thoughts to help you with your issues...

pH, hydrogen and bi-carbonates

• This is a topic I'm trying to learn. I'm daring to dream that I can build some simple models in my head that will help me diagnose these types of problems.
• Low pH means you have high levels of hydrogen ions. Which means you have a higher level of bi-carbonate to carbonates ratio for your alkalinity.
  • Increasing your carbonates (soda ash) will consume hydrogen ions to create more bi-carbonates, which will drive up your pH.
  • Phosphates somewhat impact alk also. Unclear yet how much and how other than binding to calcium carbonate and reducing alk. I think.

Idea: Why not run your tank at a 9-10 dKH for a bit and see what it does to your pH? My gut says your pH will rise into the 8.3 range where you want it to be. Please get someone to confirm this thought but I don't think there's harm if done slowly.

Draw fresh air for your skimmer from outside.

• Inside air is higher in CO2 and creates carbonic acid which drives down pH.

Consider the impact of organics on your pH.

• Create high flow to keep anything from landing on the bottom. Material in the water column eventually makes it to the sump where it's skimmed out.
• Try an inexpensive controller to change the power head flow to keep things different.
  • I put power heads low to keep everything moving.
• If you have sand, make the bed very thin. Then stir it occasionally to keep it fresh from crud.
  • I could go on all day with how bad a poorly maintained sand bed can be. I did it.
• Blow off your rocks regularly to keep everything in the water column.
• Consider removing rocks, scrubbing and starting them over. This will not remove the phoshates. It does remove organics.

Make your sump out compete your display tank. Look up this topic. It takes time to get this system going.

• Create ideal algae environment in sump. Macro algae for example. Or algae scrubber.
  • Run this at night to allow it to consume the CO2 and keep the pH higher.
  • Consumes nitrates and phosphates. Consumer you might need to dose something like chaetogro to ensure the macro algae does not have a limiting nutrient.
• Manually remove algae in display tank.
• Work these over and over until your sump is the "algae master".
  • Right now your display tank is consuming the phosphates and nitrates. Get your sump doing it instead.

Leaching from Rocks

• To start over, I did a lanthanum chloride soak to start my rocks off as fresh as possible. I'm unclear on whether this was a good idea...but I did it and nothing died (FOWLR). Now I'm focused on getting phosphates down, letting the remainder leach out, and then never letting my phosphates rise again to avoid the rock binding again.

Hope that helps.