nutrient testing

[Lora Outcelt]

So, things are going well. My indoor mini-system (30gal) is up and running (started cycling in August, added plants and seaweed extract in early september and six 1" pangasius catfish fish last week). I am successfully growing plants for the first time in many years of trying!  I have some questions regarding nutrients though. First of all, is it possible to test for nutrients like iron and other micro-nutrients? Second, if not, how do you know if you need them. (Please remember, I have never grown plants successfully, so I dont really know what plants should look like to be able to recognize problems.) Third, how do you add micronutrients other than iron (which I added by opening a human vegan chelated iron supplement and mixing half the powder into water that I added to the growboxes...about 8mg.), like copper or magnesium. What about heavy metals? are they nutrients or poisions in aquaponics? I looked into maxicrop, and while it has iron, it doesnt seem to have any other micronutrient and after looking over the nutrient defeciencies chart posted by Chi (thanks Chi) I am thinking that my plants need calcium and potassium. How do I get these to my plants?

[TCLynx]

The normal sign of iron deficiency is pretty easy to recognize though some other problems can look similar.  Anyway lack of iron (or iron being locked out by pH being too high) will look like yellowing leaves but the veins stay green at first and it starts with the new leaves first.

 

Seaweed extract generally does have trace elements but they are there as a trace so they are often not listed on the label.

 

Supplementing Calcium and potassium is often tied to pH control as well.  In most systems the pH will drop with the action of the bio-filter over time and eventually one usually needs to add some buffer to the system to bring the pH back up.  If the source water is hard water (full of calcium carbonate) then simply topping up the system with water might keep the pH up high enough but it is possible this will result in an over abundance of calcium.  I have a couple systems that I am now topping up with rain water and to keep the pH up I'm alternating adding potassium bicarbonate (find at brew and wine supply shops) and calcium carbonate (lime or chicken grit or occasional use of well water.)  Many of the big commercial operations will actually alternate the use of calcium hydroxide and potassium hydroxide but these are caustic and must be handled carefully so as not to injure ones self or use too much and cause too abrupt a pH change in the system.  Now I'll mention the danger of using natural and slower buffering materials, they are slower acting so one must not go adding more because they don't see the change after a few hours or if you do add more, add it in such a way that you can take it back out of the system.  For instance, shell grit can be placed in a stocking or paint strainer bag and hung in the tank and when the pH gets up high enough, you pull it out.

 

Hopefully this explanation was not too vague.  In general a high quality fish feed will take care of most of your plants needs though most new systems need a few doses of seaweed extract and/or iron to get them up to speed before the system has really matured.

[Lora Outcelt]

TC - Thanks for the info. I dont think it is my ph though, bc it has been sitting at 7.6 for almost a month now. The rest of my numbers; ammonia-0, Nitrites-0, Nitrates-2. My water source is Denver municiple water, with a ph around 7.8 right out of the tap and 7.6  24 hours later. But, from what your saying, if my ph is ok, then it isnt nutrient lock out, but I think, maybe, just a lack of nutrients. I have not been feeding a high quality food (I am not sure what constitues a high quality food), but just some tropical fish flakes I had on hand. And I have only supplemented with iron once (8mg) and seaweed extract once (1/4 cup for 33 gallons poured directly into tank), so I think I will just try adding more of both (though, I have to admit, I was so glad when the water started to finally clear up after the last addition of seaweed extract).

Thanks so much for being such a great resource! I always know, if the post is from TCLynx, then the info is 100% reliable.

[TCLynx]

Thanks.  You might take to doing very small doses of Seaweed more often if you don't want the water to go really dark on you.  The pH of 7.6 is functional but your plants will struggle with it, I know mine do.  My systems that I'm topping up mostly with rain water are doing far better with their pH between 6.6-7.2.

 

As for how to tell if a feed is good for aquaponics.  Well most aquarium feeds are designed to keep the fish fed while putting the least possible nutrients in the water since most aquarium owners have to do water changes to keep those nitrates down.  Most people who want the nutrients do better using feeds designed to grow fish out as big and as fast as is reasonable.  So feeds that fish breeders use may be a better choice instead of the feed you find at the aquarium shop.  Now that said, I have to admit to using flake feed for small fish occasionally and for my shrimp.

[Lora Outcelt]

ok, so I am going to start giving my tank more iron and a capful or so of seaweed extract once a week. To bring my ph down a bit, I thought I would try adding some peat moss, in a little cotton bag (for easy removal) and see if that helps. Correct me if Im wrong, but I believe the peat moss will only work for a little while, and that I should plan on replacing it occasionaly. Also, I think I might try feeding my catfish food scraps from the kitchen, in addition to the flakes until I can get some feed that will support growth.

I will let you know how it goes.

Again, thanks for any and all information.

 

[TCLynx]

Beware that the peat will tint your water too and that it will be slow acting as would something like driftwood.

You will probably have some better luck bringing your pH down by adjusting the top up water pH in a bucket before using it in the system.  I'm not really a big fan of using acids all the time but if you get the system pH down closer to 7 you might not need to keep adjusting the top up water long term but only until the bio-filter starts needing some buffering added back in.

 

so if you adjust your bucket of top up water down to between 6.5-6.8 (do this carefully a little at a time letting the water mix and testing it then wait a while and test again to see how the calcium carbonate is interacting with the acid) and use small amounts of it to top up your system it should bring your system pH down very slowly which is the safe way to adjust system pH.

[Lora Outcelt]

Thanks TC. I appreciate your advice. I am torn about which way to handle lowering my ph. Are there pros and cons to using peat moss or driftwood (the slow way) as opposed to doing it with acids(the fast way)? I think I might prefer the method that requires as little tinkering as possible. That way I am less like to mess something up! Thanks again for any input.

 

[TCLynx]

Well for using the peat or drift wood, I'm not experienced with it so I can't really say which would be easiest.

 

Doing the adjusting outside of the system where you can let things mix and settle and wait a day and check the pH again is the "safe" way but it requires some extra buckets or barrel of water on hand to do the tinkering in where you are not risking your system.

 

Some people will even use a RO filter to get rid of the excess hardness before using the water to top up their systems but I don't have one of those myself.