Water Changes

[Chi Ma]

This was split off from another discussion.

AP has been said to be a closed loop system. But as a layman, I see that we are always inputting something whether it be feed, water or extra nutrients. This extra "stuff" we are putting in has to go somewhere. The bio load (fish, plants, bacteria, etc, etc) take up this "stuff". We pull this stuff out of the system by harvesting it. But some of it stays in the water.

In AP systems we try to conserve water by just topping it off and not doing water changes . Is there a point where all this input of stuff becomes toxic? In nature it rains and floods and the water chemistry is reset. Do we as AP growers need to reset the chemistry of the water also? Wouldn't it be wise to do so to imitate nature? Lot's of people that do AP don't have the technical background or patience to test water for the hundreds of things that may affect the health of the fish/plants. Wouldn't saying that a 50-75% water change every 3 months be feasible for the health of the system? You can use the water to water your soil based crops or landscaping.

[TCLynx]

I know there are plenty of people out there who have been running AP systems for years without ever doing huge water changes like that and though I doubt most of us have every gone and tested for all the possible "bad" thing, I can say that most of our systems are still doing well.

Remember that many people are doing aquaponics because they don't have the luxury to do water changes because good water is scarce in their locations and without that luxury, they usually don't have extensive soil gardens to take advantage of periodic water changes.

If people are careful not to add alot of extra "stuff" to their water and only supplement when the plants show signs of deficiency then it becomes less likely that undesirable stuff will build up to toxic levels.

Now if some condition of the source water/media/ or portion of the system might tend to supply excess of certain nutrients then it might become important to monitor for a build up of those (example copper or zinc) but I would not personally recommend water changes just because.

Remember that large water changes are not good for the stability of systems and can cause issues like re-curing algae blooms and depending on the source water, water changes might actually promote more build up of things in conjunction with water conditioners or chloramine/chlorine neutralization. (When only doing very small water top ups in a mature system one might not need to worry too much about a small amount of treated water without neutralization but when doing a huge water change it is quite a different story.)

My big system has been full of water since sometime in Feb 2008 and I have never done a really large water change though I have occasionally had some mishaps while making changes cause the loss of some water and require extra top ups. Catfish are doing well in my system. Perhaps not too scientific but it is just a backyard system.

[Chi Ma]

Going by my aquarium experience, the tanks I have require periodic water changes. The plants and aquatic life I have in the tank can not possibly use all the dissolved solids introduced by fish food and top offs with tap water. So the TDS (total dissolved solids) will eventually get so high that the fish and plants will respond negatively. I see the AP set up as just a scaled up aquarium. For now I have the luxury of being able to turn on the tap to fill my tank. So I think I will do the water changes to emulate natures flushing from rains and floods. I have a lawn and trees that will benefit from it.

Has anyone with a mature <2-5 yr old system> test for TDS? Just because fish can live in adverse conditions doesn't mean that they should.

I wonder if some one can do a little test with 2 small 10 gallon AP systems and compare one with water changes and one without water changes with everything else being equal.

[TCLynx]

I see that "nutrient interest" as a sign that media beds may well handle a much lower fish load and provide ample nutrients for plants on that reduced fish load once the systems have a nice maturity of solids in the beds. Just a round about way of saying that when one isn't "removing" the solids, you can get by on far less fish and fish food and yet still grow the same amount of plants.

Drawback is that if one were to continue running a media bed system with no solids removal with an overlarge load of fish long term, the beds will become over burdened with solids and could become toxic to the system.

This might be why some people feel that media bed systems are not viable, because long term, they should be used with a rather modest fish load compared to a system that removes all solids but this opinion would be based on some one trying to grow max fish and not necessarily getting a balanced system. Other people have found that they can run media systems and get rather impressive long term plant growth with a very minimal fish load long term. What is best will really depend on the situation and goals for the system.

[TCLynx]

how do you suggest we test for TDS?

[Chi Ma]

Here is a little article

http://en.wikipedia.org/wiki/Total_dissolved_solids.
http://reefkeeping.com/issues/2004-04/rhf/feature/index.php



TCLynx said:

how do you suggest we test for TDS?

[TCLynx]

Exactly!

What I mean to say is that most of the things likely to build up in my AP system at least are not going to read much on a conductivity meter.

Put it this way, I've got a bluelab truncheon. My well water usually reads at below the lowest reading. If I salt a system up to 3 ppt the reading is going to be beyond the scale. Luckily, plants will use up salts slowly over time so even with a system that was once salted to 3 ppt it is now back down to reading 300-400 ppm or 420-560 ppm or 6-8 CF or .6-.8 EC.
So not only do we not really know any more that we did before taking the measure, but we don't really even know what the measurement is telling us. Basically, there isn't much salt left in the system really.

I also kinda doubt that simply doing a big water change would really make a big difference in what might be built up in my system since most of that build up will remain in the grow beds slowly breaking down.

[Harold Sukhbir]

Interesting idea on reducing the fish load as a system matures, without conclusive data on the subject we can at least consider this as a temporary solution.The intentional/unintentional experiment of Kobus and his extended growth is a good indicator of this idea of accumulation and that, only after one year! What about the people out there with the oldest AP beds in service? Is anyone utilizing this practice?

TCLynx said:

Exactly!

What I mean to say is that most of the things likely to build up in my AP system at least are not going to read much on a conductivity meter.

Put it this way, I've got a bluelab truncheon. My well water usually reads at below the lowest reading. If I salt a system up to 3 ppt the reading is going to be beyond the scale. Luckily, plants will use up salts slowly over time so even with a system that was once salted to 3 ppt it is now back down to reading 300-400 ppm or 420-560 ppm or 6-8 CF or .6-.8 EC.
So not only do we not really know any more that we did before taking the measure, but we don't really even know what the measurement is telling us. Basically, there isn't much salt left in the system really.

I also kinda doubt that simply doing a big water change would really make a big difference in what might be built up in my system since most of that build up will remain in the grow beds slowly breaking down.

[TCLynx]

I know that there are aussies out there with systems that have seasonal fish loads and some of them probably do just fine still growing plants through the summer even when the trout are not in the system.

I know I've run systems fishless for periods of time and growth continued on just fine without the fish for quite a while.

I'm not against doing a water change if there is some problem seen or contamination noticed but I don't think I could tell some one they should change out 50-75% of their water every few months. That really defeats most of the "benefits" we list about aquaponics being better than Hydroponics or aquaculture.

[RupertofOZ]

Whoa.... some many points of arguement... in the one thread....

And sorry... so many things that are WRONG...

This extra "stuff" we are putting in has to go somewhere. The bio load (fish, plants, bacteria, etc, etc) take up this "stuff". We pull this stuff out of the system by harvesting it. But some of it stays in the water.

Does it?... certainly a point that deserves some definitive emperical study... as does then whole question of "toxicity" buildup...

But, from experience... I'm totally unconvinced....

In nature it rains and floods and the water chemistry is reset

Is it?... how, and measured against what.... or is it more a matter that many of the "things" you might have in mind are merely leached further down into the soil??

Run your system for a year, then pull out all the fish and see how long you can run plants with no nutrient input. If your plants lasts for months, like mine did, then it means that stuff can build up in your system.

How can you quanitify that there was "no nutrient" input.... rain events in themselves could well provide a degree of trace elements, and nitrates are commonly formed during lightening storms....

And then... there's the worms that most of us use in our media beds.... mineralising the system.... and IMO... dealing with many of the "toxic" metallic" elements... by making them motile cations.... thus supplying the trace elements for plant growth...

And plants dont need very much in the way of trace elements to sustain growth...

Going by my aquarium experience, the tanks I have require periodic water changes. The plants and aquatic life I have in the tank can not possibly use all the dissolved solids introduced by fish food and top offs with tap water. So the TDS (total dissolved solids) will eventually get so high that the fish and plants will respond negatively. I see the AP set up as just a scaled up aquarium

Yep you're right... the type and amount of aquatic plants you have in your aquarium... almost certainly wont deal with all the TDS in the system... or even the nitrates...

Aquaponics IS NOT A SCALED UP AQUARIUM... any more than RAS aquaculture is....

We deal with most dissolved solids in aquaponics by the (relative to aquaria) large filtration volume of our grow beds... in conjunction with worms...

Here is a little article

http://en.wikipedia.org/wiki/Total_dissolved_solids.
http://reefkeeping.com/issues/2004-04/rhf/feature/index.php

The first link goes on to correctly define what TDS is.... the second is total bullocks, and shows absolutely no knowledge of what TDS is... and the general nonsense and ignorance of many in the aquaria feild IMO...

TDS IS NOT a measure of "electrical conductivity"... the measure of metallic cations...

EC IS... and as TCL pionts out, once a system is "salted"... even EC is no longer valid as a measure...

I too have a bluelab truncheon, several in fact... and used them extensively for years in hydroponics....

And I can tell you that they have remained hung on the wall for years... only being removed/calibrated and tested... whenever someone brings up the subject of EC in aquaponics...

Despite my many years and extensive knowledge of hydroponics... and 5-6 years of aquaponics... I have NEVER been able to correlate the EC readings in aquaponics with anything that I ever could in hydroponics... or anything meaningful... other than a "general" guide to plant health.... and I use the term "general"... very loosely...

and knowledge about what happens to sludge in beds over a long period of time.

What "sludge in beds"????.... if you're getting "sludge" in your beds... then;

You're exceeding your filtration capacity for the amount of feed you're using... either because you're under filtered in terms of total grow bed volume... or you're over-stocked... or both....

Worms will also take care of most of the "sludge" in a properly configured system...

I've seen this argument raised before.... and I have deliberately pulled down a bed after 2 years of service to disprove it... and posted pictures accordingly.... as have others....

I just downloaded 2 new papers produced in 2010 on aquaponics. Not had time to do more than skim the abstracts, but already there were interesting bits in it. First up, filtered water seem to outperform unfiltered water, sand as a media outperformed gravel in some short-term experiments, and in one paper, the optimal nutrient loading was found to be 15 - 45 g of fish food to square meter of plant. THAT is a big one - UVI stats say 60 - 100 grams. The intro on the paper that concluded the low nutrient loading requirements also have some very interesting things to say about nutrient stability.

Please link to the papers Kobus, or PM me... I'm intriqued as to both... the use of sand as a filter in aquaponics... and the nutrient loading aspects...

Indeed, I'm interested in their actual "aquaponics" model... and methodology... as much as their "conclusions"

Don't get me wrong... I think there is much that would be beneficial in good scientific studies regarding aquaponics....

But I think we would be best served by being specific in what it is we would like to be investigated... and then let it be examined by scientific method... rather than by extrapolation of personal experiences, or similar experiences in other fields...

[Chi Ma]

I didn't intend discussion this to be an internet pissing match. I'm new to this. I was just relaying my experiences and voicing concerns. I'm just a regular guy trying AP out. What seems to be intuitive in AP sometimes isn't. We all have different goals and reasons why we chose to use AP. If it's someone 's prerogative to do things a certain way they shouldn't be bashed because it's not in alignment with your thinking. There are many paths we can take to the same destination. There is no right and wrong way. As long as we know are destination/goal and have an open mind we can learn along the way. There is always room for improvement.

[Harold Sukhbir]

Our sludge also comprise of Heterotrophic bacteria which stores and uses nutrient as energy.

[RupertofOZ]

Sorry guys... didn't intend the post to come across as an "internet pissing match".... and I'll plead guilty to not having scrolled past the "cited/quoted" part of your post Kobus to see the attached files...

Kobus, point noted about your "enclosed" environment... but I never said that plants could be run by rainwater alone... although I do believe that many plants can/will and do...

I do believe that almost all nutrients are utilised by fish and plant growth.... removal of fish, hence removel of further nutrient input from feed.... means surely that any further nutrients that may remain in the water ... will be taken up for further plant growth... and your experience seems to bare this out...as also noted by TCL, and my own experience, and that of others.

I really do believe that the nutrient requirements for plants is actually quite low... and again my hydroponics experience leads me to believe this.... and is probably a lot lower than many might assume....

Perhaps we need to be mindful that in an AP system...by it;s recirculating nature... we are providing the plants with all/most their nutrient requirements... all the time....

And they uptake what is available, when required... and growth rates and yields directly reflect this...

I do agree that there is work to be done to "quantify" many things .... including possible "toxicity" buildup.... but in comparison to both fertiliser applied soil agriculture, and nutrient supplied hydroponics... the nutrient provision to plants in aquaponics is, and it is my opinion.... significantly lower... and respectively less likely to exhibit any "toxic" buildup that might be reflected in either or both of the other production techniques...

Have you run a detailed analysis of the sludge in your system after 6 years to say that there is nothing left? I will attach a pier reviewed paper to tell you where it goes in aquaculture. 30 - 90% is in sludge. What we are theorizing on is what percentage of this can the plants handle. Worms cannot make it dissapear. Both papers are pier reviewed out of Elsevier. I rate that above Wikipedia.

Kobus, firstly I've not fully read the attached paper.... which I will... but I make these points...

After 6 years... the just isn't any real degree of sludge buildup in my grow beds... and TCL, Joel Malcolm, Murray Hallum and others, will tell you the same thing.... and we are all pretty sure that indeed it is the action of worms in our grow beds that contribute to this...

Secondly, I'm not in any way disregarding the fact that fish produce wastes... or "sludge" as you, and possibly the paper linked to, suggest...

I've yet to fully read the paper, so I'll not comment on the figures of 30-90%.... because I don't know what they pertain to...

But the paper seems to suggest that the "hydroponic troughs" were utilised, without plants... as a means of settling out and capturing the "sludge".... uneated feed, fecal matter etc... in much the same way as a settling tank/clarifier/swirl filter might be applied in a RAS operation... and that is what this paper represents... a RAS operation... not an aquaponics system...

And I'm happy to acknowledge your studies in geology.... and fully embrace the concept of peer reviewed papers...

But I didn't make my comments based on "Wikipedia".... but on many years of commercial hydroponics operations, 4-5m years of aquaculture studies (with distinctions, for what it's worth)... and many years of aquaponics experience...

I never expected or stated that in either my experience, or others... that all about aquaponics is known... or has been reviewed or published... indeed not enough has...

But your claim to knowledge by a degree of seperation from a friend... rather than that of your own experience Kobus... would be as baseless as any such claim i might similarly make...

P.S... I did begin my university studies with a view to becoming a research chemist.... while I didn't continue that direction, and don't hold any formal qualifications, remaining just a mere "pleb"... I think I do have a degree of chemical knowledge.. for what it's worth...

No one is obligated to accept any, or all of what I post... and I'm happy to be challenged on anything...

I offer it based on my experience, and similar experiences of many others who have frequented other AP forums for many years....

Chi, my remarks regarding the distinction between aquaponics and aquaria might have been interpretable as a bit heavy handed.. but weren't meant as a personal attack as such...

I do get somewhat disturbed at the recent trend towards treating aquaponics systems as aquaria, with all the associated treatments and general nonsense... that seems to have become prevalent of late... because I think it is dangerous to do so...

Aquaponics is more akin to RAS aquaculture... and principles involved... rather than aquaria...

And I'm happy for anyone to pursue whatever direction and way of doing things that they might wish to... but I point out things at times that I think might either help... or prevent a disastorous fish kill