PO4 Source Experiment

[kjmsmith]

I realize there are a number of current and archived threads on reasons for elevated PO4 but I am posting this one looking for feedback on a recent experiment I did on my system to challenge or validate my results. I apologize in advance for the lengthy post but want to be sure I include as many details as possible relevant to this topic.

Before a brief overview of my system, be warned it is a sumpless set up with a canister filter. I put that out there because it seems whenever sumpless systems are discussed in relation to high nutrients, the responses are usually advice to install a sump, canister filters are 'nitrate factories' etc so I am hoping not to be given such advice but rather opinion on my system as it is.
Background:
- 90 gallon mixed reef established for 8 years - started as a 55g and then moved contents to 90g 6 years ago
- light bioload with 6 fish - 1 regal tang, 1 foxface, 2 ocellarious clowns, 1 six line wrasse, 1 yellow tail damsel
- mostly lps - branching hammer has always grown like a weed and some sps with mixed results
- 1 BTA that is the size of a dinner plate
- Reef octopus BH-1000 HOB Skimmer with excellent skimmate production
- Fluval FX-6 with filter pads and 2 trays of matrix
- 3 koralia powerheads
- 2 Ocean Revive T-247 LED's running 35% white/red/green (6 hours/day) and 50% blues (8 hours/day)
- apx 50lbs live rock - some from a dead tank I received when I first started 9 years ago, other pieces added over the years as well as 2 or 3 hunks of marco - last piece added over 2 years ago
- 40lbs of aragonite caribsea seafloor special (added as new sand when upgraded to 90g 6 years ago)
- small intank 'fuge' with a couple mangroves and chaeto (probably not enough to make any measurable difference to nutrient control)
- feed 1.5 cubes of frozen mysis daily, rinsed in RODI - all food gets consumed
- dose Aquavito Fuel - 1/3 the recommended dose, once/week
- dose 10ml phytoplankton and zooplankton twice/week
- typical CUC of snails and crabs
- water tests with Salifert kits
Being sumpless, my system has always been a high nutrient system with NO3 averaging 50ppm and PO4 averaging 0.25ppm. KH runs about 7-8 - I manually dose soda ash every 3 days or so to maintain, Ca is usually 400-430 with no need to dose and Mg at 1200-1300, again no dosing. I don't test pH. NaCl is kept @ 1.025 and I use Aquavitro Salinity since day 1 with this tank. I did use other brand salt for about a year last year when I was unable to source the AV but was able to find a new supplier and switched back. Back in January I started seeing diatom blooms and water testing showed a rise in PO4 which peaked at 2.0 ppm. I had made no changes to the tank or husbandry practices that would have lead to this. At that time I lost some acros. I started doing large water changes with no effect. I ran some Phosguard in the canister and it lowered a bit but stayed between 1-2 ppm. I decided at that point to try carbon dosing with vinegar to try to reduce NO3 which was 50 and hope to have an eventual effect on PO4. While trying to manage this, I decided to move my tank to a new stand which I thought was a great opportunity to do a full tear down, clean and see if I could get the PO4 down. 3 months ago I did this which included a heavy rinse of the sand in tap water and then flushed with the old tank water. I reused about 50% of the old H2O and the remainder was new. I removed apx 40 lbs of rock (from 90 down to 50lbs) to rescape and improve flow. The last piece of vital info is that I have used an RO system since day 1 and change filters regularly. I didn't test for TDS which I know I should have been doing. While the RO had zero NO3 and zero PO4, I recently did a TDS test and it showed 14. Understanding the diatoms may be from silica in my water source combined with high PO4, I installed a DI filter 4 weeks ago. My TDS has now been 0. Despite large H2O changes and even running PhosBond in the canister, ny PO4 is staying between 1-2 ppm and NO3 is down to about 20ppm. I had reached a point of 60ml vinegar per day with no results but I started developing cyano so I gradually reduced the carbon dosing and have now stopped it completely as it was having more negative effects than positive.

Finally on to the experiment.
My hypothesis is that the source of the PO4 is not coming from my water source, salt source or overfeeding. I suspect 'old tank syndrome' where the PO4 is leeching from an in-tank source that has been exposed to high nutrients for 6-8 years.
To challenge this I made 1 gallon of fresh salt water from my RODI mixed to 1.025. I tested this water to have 0 NO3 and PO4. I then added a 2-3 lb piece rock that I have had in my tank since the start and circulated it in a bucket with a powerhead. After 24 hrs there was still no measurable NO3 or PO4. After 48 hours the same. I then removed the rock and using the same water I added apx 2 cups of aragonite from my tank (drained out tank water) and circulated. After 24 hrs the PO4 is already 0.5 ppm.
My conclusion is that the aragonite is the source of the leaching PO4.

My question to the members - is this a fair conclusion? If no, what haven't I considered? If yes, is it best to remove the substrate and replace it with new or wait it out for the PO4 to be exhausted and it will come down eventually?

Thank you in advance.
Kevin

 

[ZaneTer]

Your aragonite is the source.

It’s also the source of a stable supply of PO4 to your tank. Many studies have been done on aragonites adsorption and desorption properties relating to PO4.

A small amount of aragonite is capable of holding and releasing huge amounts of PO4.

I read a study recently involving dolomite.
0.2g of dolomite in 1l of water could pull in 5ppm.

For your tank that would only require roughly 70g which is quite far from your current 40lb of aragonite.

@jda did a great study on aragonite and PO4

 

[jaxredsoxfan]

I think you approached that wisely and seem to have determined the source. I would trust those results. The question now becomes do you want to replace the sand? There are several posts here in regards to full changes. I might try that. Good luck and great job doing the diagnosis!

 

[kjmsmith]

Thank you for the feedback. I think I am going to change out the sand and have done some reading however I would welcome any advice. I plan to remove the current sand slowly by scooping and sucking it out without creating much of a mess. Once its all out I will replace it. My questions to the group;
- should I remove all of the current sand all at once or remove portions of it over a period of several days to reduce chance of further or sudden water imbalance?
- once removed should I leave the tank bare bottom for a few days and do water changes to get the PO4 down before adding new sand?
- I plan to replace it with new Caribsea aragonite - do I want to use the regular dry or the Arag-alive? - obviously I dont want the tank to cycle
- should I add the sand slowly ie 5lbs/day over 8 days or add it all at once?
Many thanks!

 

[taricha]

To challenge this I made 1 gallon of fresh salt water from my RODI mixed to 1.025. I tested this water to have 0 NO3 and PO4. I then added a 2-3 lb piece rock that I have had in my tank since the start and circulated it in a bucket with a powerhead. After 24 hrs there was still no measurable NO3 or PO4. After 48 hours the same. I then removed the rock and using the same water I added apx 2 cups of aragonite from my tank (drained out tank water) and circulated. After 24 hrs the PO4 is already 0.5 ppm.

Very cool! could you extend this test for us by one step?
exactly what you just did:
1 gallon of "zero" water, add your cup of aragonite from tank, measure 24hr later. (got 0.50ppm PO4)
Then do 100% water change with another gallon of "zero" water.
measure 24hr later (will it be close to 0.50, or a small fraction of that?)

I think people are increasingly aware of the concept that aragonite can hold and release large amounts of PO4. (hat tip @jda thread) But some people say it can leach large amounts endlessly, but other things I've read say about 80% gets released in the first 24hr.

 

[kjmsmith]

Very cool! could you extend this test for us by one step?
exactly what you just did:
1 gallon of "zero" water, add your cup of aragonite from tank, measure 24hr later. (got 0.50ppm PO4)
Then do 100% water change with another gallon of "zero" water.
measure 24hr later (will it be close to 0.50, or a small fraction of that?)

I think people are increasingly aware of the concept that aragonite can hold and release large amounts of PO4. (hat tip @jda thread) But some people say it can leach large amounts endlessly, but other things I've read say about 80% gets released in the first 24hr.

Sure I can do that, I still have the sand in the bucket of current H20 - I measured it last night after 48hrs and it was between .5 and 1.0. I’ll do a complete H2O change and keep the same sand and see what the values are tomorrow :)

 

[jda]

The release is not endless, but it sure can seem like it.

It will only release back to "equilibrium" with the water... aragonite will not release all of it at once. It acts as a buffer, which can be good in some situations, and bad in others. This is good when you are near NSW levels when the aragonite will buffer if you get too low ensuring that you never really bottom out... but band when it has become a nearly impossible task and you might need several 5g buckets of GFO to get rid of it.

It seems that it will release all that it will release in a few days. The stuff on the surface releases very quickly, but the stuff more in the middle needs more time - this depends on the porosity of the media type and how gunked up it is with organics.

I have a whole rant about old tank syndrome being a result of the reefer slacking and the aragonite unable to mask their lacking care any longer... I will save this for another day.

Here is the snippet from my thread after a weeks of testing:

Running total: 25.3ppm total in water column nets .1533 ppm left after aragonite absorption.
...
Total: 57.4 ppm in water column to .1748 ppm after aragonite was introduced.

Boring read, mostly and it kinda went off the rails in parts:

Phosphate Absorption Rates in Aragonite

I was chatting with @mcarroll the other day about phosphate binding to aragonite. I have seen many instances where phosphate bound live rock and sand requires massive amounts of media and water changes to remove all of the phosphate. Two instances: 1). Local purchased 120lbs of Pukani live...

www.reef2reef.com

Once you understand how much the aragonite will bind and how hard it is to get back out, you can see why I am so perplexed that people add this to their tank on purpose. To each their own, but I doubt that most of them understand what they are doing.

 

[jda]

As you can see in the quote/snippet above, the binds are exponential, which is what Dr. Holmes-Farley said in the beginning. The more that you add, the more will bind.

More than twice the introduced phosphate only moved the water concentration about .0215 from .1533 to .1748.

 

[kjmsmith]

Boring read, mostly and it kinda went off the rails in parts:

Phosphate Absorption Rates in Aragonite

I was chatting with @mcarroll the other day about phosphate binding to aragonite. I have seen many instances where phosphate bound live rock and sand requires massive amounts of media and water changes to remove all of the phosphate. Two instances: 1). Local purchased 120lbs of Pukani live...

www.reef2reef.com

Well that was quite the read :oops: my head hurts lol...I guess this now begs another consideration - whether I should even be replacing with aragonite or should I be using crushed coral or ??? I don't think bare bottom is a look I want.
Ill report back tomorrow with the updated levels... thx for all the info!

 

[jda]

If you do decide to replace it, that can help with the phosphate, but you can have other unintended consequences. The sand is functioning in other ways, so you must replace it slowly and in small chunks. ...like probably no more than 20% every few months. Otherwise, you can lose all of your anoxic bacteria places and stuff. Plus, you need time for the microfauna to populate the new areas.

IMO, a mixed grain reef sand is better than crushed coral for reefs.

I do like the sand to buffer the phosphate, which is why I will always (for now) have 2-3 inches in all of my tanks. I just like it to buffer in the 1-3 ppb range, not ppm.

Since both your N and P are high, maybe a slow and methodical regiment of organic carbon might be a good idea - sugar, vinegar or vodka. Too much can be an issue. Closely monitor and once you get down to 5ppm of N and/or .10 of P, then you have to stop and then switch to something like chaeto, which will be WAY more effective with lower N and P levels. Using organic carbon to go too low is a disaster, but it can be a good tool when used with a good protein skimmer and with a large dose of patience and intelligence.

If you have room in your sump for another skimmer, get one. It can really help too.

 

[Randy Holmes-Farley]

My conclusion is that the aragonite is the source of the leaching PO4.

My question to the members - is this a fair conclusion? If no, what haven't I considered? If yes, is it best to remove the substrate and replace it with new or wait it out for the PO4 to be exhausted and it will come down eventually?

Foods are nearly always the main source, overfeeding or not. In your case, the aragonite may be a contributor but still may not be the main source and also may not be any significant original source.

As folks have indicated, aragonite in water that contains phosphate will bind some of it, and if you then put that into clean water, it can come back off again, making the aragonite look like a source (and it sort of is), even though originally it may have had none.

That said, some aragonite may have substantial phosphate before adding it, and it can be a primary source, at least for a little while in a new tank.

 

[Randy Holmes-Farley]

Well that was quite the read :oops: my head hurts lol...I guess this now begs another consideration - whether I should even be replacing with aragonite or should I be using crushed coral or ??? I don't think bare bottom is a look I want.
Ill report back tomorrow with the updated levels... thx for all the info!

Crushed coral is aragonite, although I get your intended distinction.

 

[kjmsmith]

Very cool! could you extend this test for us by one step?
exactly what you just did:
1 gallon of "zero" water, add your cup of aragonite from tank, measure 24hr later. (got 0.50ppm PO4)
Then do 100% water change with another gallon of "zero" water.
measure 24hr later (will it be close to 0.50, or a small fraction of that?)

So after 24hrs PO4 = 0.25. I am still circulating it and see if it goes up anymore after 48hrs.

Since both your N and P are high, maybe a slow and methodical regiment of organic carbon might be a good idea - sugar, vinegar or vodka. Too much can be an issue. Closely monitor and once you get down to 5ppm of N and/or .10 of P, then you have to stop and then switch to something like chaeto, which will be WAY more effective with lower N and P levels. Using organic carbon to go too low is a disaster, but it can be a good tool when used with a good protein skimmer and with a large dose of patience and intelligence.

I did try vinegar dosing for apx 6 months following the dosing chart found on many sites. I was up to the max 66ml/day for my size water volume and was seeing no substantive changes. My acans started receding, diatoms got worse and cyano started taking over so I slowly reduced the carbon dosing and stopped completely apx 4 weeks ago. My acans look much better.

Foods are nearly always the main source, overfeeding or not. In your case, the aragonite may be a contributor but still may not be the main source and also may not be any significant original source.

Thank you Dr. Holmes-Farley, I agree the origin is likely food over the years - there were periods when I was supplementing frozen with flake from an auto feeder that was likely putting too much waste in the tank. I took that offline quite awhile ago and stick to the 1.5 cubes per day and 1/2 sheet of nori on a clip. I even started rinsing the PE Mysis thoroughly although I still am not sure that what phospahte amounts might be included in those cubes is enough to maintain the levels I’m seeing in 90g of water. I have been doing 25% H2O changes q 14 days for the past 90 days along with the Phosbond with no results which is what is leading me to the leeching substrate. I feel if I could get a handle on the PO4 reservoir (if in fact it is the aragonite), my low input of phosphates can be managed with the water changes. I would just like to get them back to around 0.25, Im not trying for zero.

Crushed coral is aragonite, although I get your intended distinction.

Huh, I admit I thought there was a difference. I was thinking aragoinite was more of a crushed rock/sand and crushed coral was, well...crushed dead coral. Is the term ‘aragonite’ applied to different substances used or are they truly one in the same?

 

[taricha]

So after 24hrs PO4 = 0.25. I am still circulating it and see if it goes up anymore after 48hrs.


Huh, I admit I thought there was a difference. I was thinking aragoinite was more of a crushed rock/sand and crushed coral was, well...crushed dead coral. Is the term ‘aragonite’ applied to different substances used or are they truly one in the same?

Thanks for data!
Aragonite and calcite refer to two different structural arrangements of calcium carbonate.
They have the same chemical formula and ratios.
Aragonite is the form made by corals. Some bivalves do calcite, or a mix. Aragonite sand has a likely coral skeleton origin.

 

[kjmsmith]

So after 24hrs PO4 = 0.25. I am still circulating it and see if it goes up anymore after 48hrs.

I missed measuring at the 48hr mark but after 72hrs the PO4 level was still at 0.25. So conceivably, as long as one is not importing phosphates at a rate equal to or greater than the current tank level, water changes and other mechanisms to remove PO4 would eventually lower. The unknown is how much water and chemical would need to be changed and at what rate in relation to how much is bound to the aragonite. I dont think my simple experiment can answer that question so I have decided that I would rather change out the substrate rather than wait this out which may take months or maybe even years.

Here is my plan, happy to hear and comments or alternate suggestions;
1. Slowly suction out current aragonite. The depth of the bed is apx 1” and I plan to remove 25% per week over the next 4 weeks.
2. Run the tank barebottom for a week and monitor parameters.
3. Add 10lbs of new Arag-alive Special Grade Reef per week for 4 weeks to total 40lbs.
4. Enjoy a more balanced tank :)
Thanks to everyone for the assistance.
Kevin

 

[ZaneTer]

I missed measuring at the 48hr mark but after 72hrs the PO4 level was still at 0.25. So conceivably, as long as one is not importing phosphates at a rate equal to or greater than the current tank level, water changes and other mechanisms to remove PO4 would eventually lower. The unknown is how much water and chemical would need to be changed and at what rate in relation to how much is bound to the aragonite. I dont think my simple experiment can answer that question so I have decided that I would rather change out the substrate rather than wait this out which may take months or maybe even years.

Here is my plan, happy to hear and comments or alternate suggestions;
1. Slowly suction out current aragonite. The depth of the bed is apx 1” and I plan to remove 25% per week over the next 4 weeks.
2. Run the tank barebottom for a week and monitor parameters.
3. Add 10lbs of new Arag-alive Special Grade Reef per week for 4 weeks to total 40lbs.
4. Enjoy a more balanced tank :)
Thanks to everyone for the assistance.
Kevin

I’m sorry but that idea won’t work to remove the PO4 very well.

You will remove 25% of aragonite at 0.25ppm. The new aragonite will balance with the old in about an hour to reach equilibrium at 0.1875ppm PO4.

The next change results in 0.14ppm
The next change results in 0.1054ppm
The final change leaves you with 0.08ppm

4 changes of 25% WILL NOT give you 100% change.

Sorry to be blunt but it’s better to know this before you start so you can make an informed decision.

Hope this helps

 

[kjmsmith]

Thx - I guess I wasnt clear in my steps. I plan to completely remove all of the old substrate before adding any new. The 7 days in between with no substrate at all is intended to see if or what the PO4 goes down to and balances at before starting to add the new. Does this now make sense?

 

[ZaneTer]

That makes perfect sense! Keep us informed about how it goes.

My apologies. I completely glazed over your step 2.