nitrates, cycling and plant fertiliser ?

D

Darwin

AC Members
Feb 4, 2006
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Australia
Hi all,

A little bit over a week ago I crashed my biofilter about 10 weeks after starting up my 20G tank (the tank was cycled when it happened). The tale of that saga can be found on this thread if you're interested;

http://www.aquariacentral.com/forums/showthread.php?t=68801

Anyway, over the last week since the crash I have kept my ammonia levels between 0.25 and 0.5 ppm with very frequent water changes and about three days ago the ammonia levels started dropping and are now 0. However, I am yet to see any nitrite. About three days ago I started seeing nitrate (between 5 - 10 ppm).

I had thought that the presence of nitrate, despite no nitrite, indicated that the cycle was progressing well. I wondered if the lack of nitrite could be explained by the nitrite-nitrate bacteria surviving. However, today it occured to me that three days ago I also started adding aquarium plant fertiliser because my plants weren't looking so good and maybe the nitrate I was seeing came from the aquarium plant fertiliser. Sure enough, I tested some tap water (no nitrate usually) with the fertiliser added and it was off the scale for nitrate.

So now I am thinking that my cycle could be going nowhere afterall! I am going to stop with the plant fertiliser and see what happens to the nitrates but what I was wondering is;

Do all aquarium plant fertilisers contain nitrates ? It seems strange to add something to the tank that I am supposed to be getting rid of with water changes ! I had a look today at the LFS and none of the fertilisers actually say what is in them.

Also, is this a common problem - that people muddle up where they are in the cycle because of unknowingly adding nitrates when they add fertiliser ?

Thanks.
 
Nitrate is a macro nutrient for plants. They *need* it in order to grow, which is why it's in that fertilizer.

In most planted tanks we try to keep the nitrates at 10ppm so that the plants have enough food to out-compete the algae. If nitrates bottom out, reach 0 ppm, too often or for too long, algae will take over (just ask me about THAT one! I've learned this stuff the hard way. ;) )

Since you have plants, you can shoot for 10ppm NO3 as a bottom number. Use the ferts to maintain that number.

Anything in excess of 20 ppm is too much and anything over 60 ppm can jeopardize your fish -- the higher, the worse it is.

Roan
 
I did a bit more research and there seems to be a bit of conflicting info regarding fertilisers.

There seem to be some people who think that there should be enough micro and macronutrients from the fish water, fish food and tap water for the plants. But I don't think this is the case for me, as all the new growth on my anubias is getting yellow spots and holes and falling off before the leaves even reach 2 cm long.

I checked the water parameters on the local water providers web site and the amount of potassium and iron in the tap water are very low. I am thinking about getting my husband to bring home from work some potassium sulphate that I can add to the tank with out increasing the nitrate content (both he and I are chemists, and am I a quite embarrassed about how poorly I have managed the water chemistry in my tank !!).

Given my lack of success so far, and the possibility that my tank hasn't finished cycling after the crash - should I leave fertilisers alone at the moment ?

Perhaps I should check out the plant forum....or maybe I am just getting myself into more trouble !!
 
Please! By all means check the Plants forum. There's a huge sticky in there on fertilizers. There are also many plant gurus who post in there that do not venture into other forums.

Potassium is a macro nutrient and is much needed by plants. There are recommendations in the Fertilizers sticky thread on what to use and in what dosages.

Don't neglect the plants' needs while you cycle. They need food, too :)

Roan
 
Darwin, like most things, there's no straightforward answer. In a low light tank with water from a mineral-rich source often the fish and their food will provide sufficient macros. In a high light tank with water from pretty much any source, macros will go to 0 ppm fairly quickly (assuming good plant growth), so these must be supplemented. However, if the water is from a mineral-rich source then water changes may provide sufficient calcium, magnesium, and traces. Our water supply here is very "soft" - mineral-poor - so I need to supplement Ca and Mg. Furthermore, the level of Ca and Mg depletion is seasonal, in the winter (presumably due to the cold weather decreasing the mineral content of the water) I have bigger problems with Ca and Mg. Right now CaCl2 crystals dissolve almost readily in warm tap water, in the summer it's a struggle.

What I'm getting at is that every tank has its own unique requirements, some caused by the hobbyist (increasing lighting, plant biomass) and some by the water supply. It's up to us, the budding aquatic horticulturalists, to diagnose and provide the plants with their requirements.

If it'll make you feel any better, I did my BSc in chemistry and am studying Chemical Oceanography and still did appallingly poorly with aquarium chemistry until that fateful day when I smacked myself in the head and said, "What a minute, I'm a chemist, I know this stuff, so why am I taking advise from the monkey at the big-box store who's selling me bottles to solve my problems..."
 
happychem said:
If it'll make you feel any better, I did my BSc in chemistry and am studying Chemical Oceanography and still did appallingly poorly with aquarium chemistry until that fateful day when I smacked myself in the head and said, "What a minute, I'm a chemist, I know this stuff, so why am I taking advise from the monkey at the big-box store who's selling me bottles to solve my problems..."
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And thank goodness you did! If you hadn't, we wouldn't have all those cool answers to perplexing water chemistry ;)

Or, Darwin, put yourself in my shoes: I know absolutely nothing of water chemistry but what I've learned here from people like RTR, happychem, Daveedka and a few others. You've got a huge jump on a lotta people on here. Lucky you!

Roan
 
Darwin, while you're misappropriating lab chems, find out from your local water utility if they use chloramines in water treatment. If they don't, get ahold of some sodium thiosulfate. Mix a 30 g/L for a dechlorinator, 1 drop per gallon to be treated. In fact, since it does dissociate with time, you may want to mix a smaller volume, since 1 L would last a long time on a smaller tank.
 
Hey thanks - I don't feel like such a disgraceful chemist now !!!

My water doesn't use chloramines - just chlorine. Thanks for the tip about sodium thiosulphate - it is funny (and a bit hopeless) how I haven't transfered 'work' knowledge to the fish tank. I have used sodium thiosulphate so often for working up reactions that used halides, and just didn't put it together with chlorine in tap water !!

Before I start tinkering with the water chemistry using misappropriated lab chemicals, I think I've got a bit more research to do ! In the meantime I picked some aquarium plant fertiliser today that doesn't contain nitrate or phosphorus (wasn't cheap though ).

I get the point about each set up being different in terms of what needs tweaking, but is there a nice list of optimal concentrations of macro/micronutrients (I haven't found one yet) ?

If I had a good list - and a nice set of scales at home (I don't work in the lab any more).....just imagine the disaster I could create.

And Roan - you might not have a chem background but you singlehandedly helped me through my tank of 'milk' disaster and put me on the right track about buffering! Thanks again.
 
Darwin said:
I get the point about each set up being different in terms of what needs tweaking, but is there a nice list of optimal concentrations of macro/micronutrients (I haven't found one yet) ?
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Optimal, no, because every tank is different ;) Did you read the ferts sticky in the plants forum?
If I had a good list - and a nice set of scales at home (I don't work in the lab any more).....just imagine the disaster I could create.
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There are three ways you can do this: buy expensive fertilizers, buy products that contain the nutrients you need (Stump remover for nitrate, NuSalt for potassium, Fleet Enema for phosphate and so forth) or you can buy dry mixes.

I've not had much luck with getting the right stump remover et al, so I went with dry ferts.This kinda thing should be right up your alley ;)

I bought my KNO3 (which I think you indicated you didn't have) from www.GregWatson.com
One pound is only $2 and change. I was mixing solutions, but now I'm dosing dry. Currently I'm dosing about 40ppm nitrate (from the KNO3) every second day, and Flourish on the off days. I add some Fe every week with a Flourish dose, but not a lot. I don't dose PO4, cause I get 2.0 ppm out of the tap. By the third day I'm down to 1.0 ppm PO4, so I do water changes on the 4th day.
And Roan - you might not have a chem background but you singlehandedly helped me through my tank of 'milk' disaster and put me on the right track about buffering! Thanks again.
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Thank you and you're welcome.
Roan
 
I did read the sticky and to be honest I found it a bit overwhelming. I guess one the problems I see is the degree of trial and error.

I mean it doesn't seem like most people have test kits for every macro and micro nutrient (i can't even imagine the expense) so if you go by your water suppliers specs that is a good start but presumably you are getting some additional nutrients from food and waste and this will differ from tank to tank. I guess the margin for error can't be too small.

The other thing is that I am guessing that the reason the particular chemicals specified in the sticky have been chosen as sources for potassium etc is because they are easily obtained for the average person. But are they really the best source for each situation ? The reason I ask this is because I am adding sodium bicarb to the tank at the moment to increase my KH (until crushed coral starts to dissolve) - well I got my husband to bring me home some potassium bicarb so i could use that instead of bicarb (two in one; increase KH and potassium at once - haven't added any yet). But I haven't seen any mention of potassium bicarb in the discussions, which makes me a bit nervous.

When you are doisng with KNO3 is that for the potassium or the nitrate or both; I am still a bit confused about why you would need to add nitrate unless you had an massively planted tank (couldn't you just add another fish !!!)

Basically, I think I need to do alot more research and from what you're saying know alot more about my tanks parameters if I am going to be in position to start adding my own concoction of chemicals to the tank AND have the fish survive !

Sounds like I am going to have to buy another test kit or two (at least a phosphorus test kit cause my water supplier doesn't list that on their web site).

Is it worth buying a test kit for iron (my water supplier claims 0.02 ppm in the tap water) ?
 
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