Backyard Aquaponics
A place to discuss aquaponics

Once a system is cycling, and all readings are 0, how long after you feed fish canl you be able to measure nitrate before it gets used up by plants?

Depends on how many plants you have. If you have plenty of plants, the nitrate levels might stay so low that the are untestable/ continuously give a zero reading

Yup, I never get nitrate readings

Isn't it a slightly better system for the plants if you can maintain some nitrate in the water?

Not if you want healthy fish
But if I got zero nitrate for a long time, I'd get more fish - that is, if my climate isn't at hot or cold peaks AND if I have enough space in the fish tank for them to move around.

Nitrate does not harm fish unless it is at extremely high levels. like 800++

So this means if my nitrate levels are rising off zero then the system must have cycled? Not many plants in the system to use them up at the moment - just sprouted seedlings

Nitrates at 0 leads me to believe that the plants may not be getting enough, or algae may be taking it from them. I don't want to add more fish only to find out in a week that my nitrites won't go back down to zero.

Until recently (when I lost half my fish from doing something stupid), my nitrites remained at .25-.50. I figured it was due to less than 1:1 ratio but haven't been able to fix that yet. Maybe I could add one fish per week or two and keep checking readings and stop once the nitrite moves from zero. But at how long after feeding could I measure this movement to be sure I don't miss the measurement? I don't want to wait too long only to find out it will not return back to 0. Hence, the dilemma.

Thorn, you have me totally confused...

Nitrates at zero.... don't necessarily mean that...

The plants don't have sufficient nutrients... they may in fact be perfectly adequate, and just utilising everything available....

It doesn't mean that you can necessarily add more fish.... that's a matter of bio-filtration capacity, water turnover and oxygen provision...

It may mean that you can increase your feed rate, moderately and within test results...

As far as nitrites and adding more fish...

If you nitrites haven't reached zero... you probably haven't fully cycled... in which case your nitrates will increase once you have...

If you have cycled... and your nitrites begin climbing.... or remain above zero... it represents an imbalance... for one reason or another...

Adding more fish to an unbalanced ... or under-filtered system ... is a recipe for sudden spikes and possibly mortalities...

Waiting for the nitrites to return to zero... isn't a bad thing.... not getting to that point might be... as above...

Perhaps you're typing and transposing nitrites and nitrates within the same post???

No transposing. I had cycled, added fish, then my nitrites never hit zero until recently. So yes, probably an unbalanced growbed ratio. My nitrates on the other hand went as high as 40+. And now they are at zero which means they were used up by plants or algae. I tried to feed a little more but the fish didn't eat more. That's why I figure I could add a single fish every so often so long as the same conditions exist.

Nitrates at zero could mean that there is plenty for plants. But it could also indicate that there is not enough for plants and it will not be noticeable right away until some damage is done and plants start looking different. That is why I think nitrates at 5-10 would be perfect. Little more or little less and you can easily adjust the amount of feed accordingly to keep it in the minimal range. (But I need my fish to eat more first to do that, heh.)

Keep in mind that nitrates could also fluctuate based on season and plant load/needs. If your plants are growing well then they are probably getting what they need. Sign of too little nitrogen is often slow/no growth and older/lower leaves yellowing/dieing followed by general yellowing of the plant. (Keep in mind that there are other deficiencies that will have yellowing as a sign but where and how the yellowing happens helps tell the difference. Like Iron deficiency will first show up as yellowing in new growth but the veins of the leaves will remain green at least at first.)

Be careful not to stock past your grow bed's capacity to filter. Just because you might be able to keep adding fish now, what happens when the fish grow? As weather changes and fish grow they will eat more or less and you just have to kinda balance the plants with what the fish and bio-filter can provide.

Ditto to TCL....

It's not uncommon for a balanced, mature system to run with readings of 0,0,0....

And bearing in mind your system is relatively new... IMO.... you should just let it settle in for six months and grow out your current fish stock...

Any deficiencies can be addresses if need be.... and a monthly dosing of Seasol/Maxicrop will boost any shortfall in trace elements/minerals... and even a little nitrogen...