How many fish do I need?

[Beth Medeiros]

Our system is 2 months old.  We have a 3 bed/1 fish tank IBC system outdoors in TX.  Harold was awesome in helping us with cycling the system (since we had 3 freezes between April and May that kept sending our biofilter back into hibernation!).  Yet now, instead of too high numbers, we can't seem to get any!  The biofilter is working overtime and the plant growth over the last two weeks has been tremendously crazy.

Our problem is now this....the system cannot keep up with the nitrate demands of our plants.  Our daily readings are 0 Ammonia, 0 Nitrites and 0 Nitrates.  Our pH is around 6.3-6.5.  The iron is about 1ppm.   I am feeding the fish three times a day.   We have 10 6-8in tilapia and 22 2in tilapia.  Even an hour after feeding, I'm barely seeing ammonia at .1ppm. 

How many fish do we need to provide enough nitrates for the plant?  Is there even a way to determine if there is a deficiency? 

Our tomato plants are showing yellow lower branches at the same time that they are flowering. They have also grown 8 inches in 10 days. The reason that we were thinking that it was a nitrate deficiency was that our lettuce and other plants were also experiencing yellowing. Our zucchini are not growing (though I think that's more of an issue of non-pollination than anything else) and our beans and peas are growing.

Do we need more fish?

 

[George]

Vlad, I follow you.  Unfortunately, by weight, so I added almost twice as much magnesium as iron, 10% / 6%.  

Thanks.  

[Larry Alesi]

You might want to try a nutrient calculator like the plant people use in the Aquarium hobby. http://calc.petalphile.com/

I use this for my planted tanks and along with the plant deficiencies chart that was previously posted. It's important to remember when adding supplements to a contained system that you may reach the desired level very quickly. I also have a lot of water test kits that I use to monitor different additive levels.

   

[Vlad Jovanovic]

I wouldn't worry much about that George, since most plants need way, way more Mg than Fe. It's super-duper-ultra unlikely that you've 'hurt' anything yet  

George said:

Vlad, I follow you.  Unfortunately, by weight, so I added almost twice as much magnesium as iron, 10% / 6%.  

Thanks.  

[len pierce]

Vlad,

At your suggestion, I have replaced my liner with a "Fish safe" liner from a local supplier.  I have washed out my media beds and have started cycling again using ammonia. I added river water at a pH of 6.9.  Should I add some sea salt for the minerals mentioned.  If so,  how much volume , ie.  a teaspoon? to 180 gal tank?  What about seaweed liquid with Iron as well to help the plants continue to grow?

[Vlad Jovanovic]

Yup, liquid seaweed extract with iron will help the plants continue to grow. Is your fish tank 180 gallons, or your total system water volume? If it's your total water volume then we'll call that 180 gallons... 700 liters...

So at 700 liters 350 grams of total salt would be 500ppm...So roughly 140 grams of sea salt, 140 grams of KCl and 70 grams of Epsom salt should be fine...

River water huh?

[len pierce]

Thanks Vlad,

Yes, I piped it out of the wenatchee river (I have irrigation from the river) and the total is 180 gals.