Backyard Aquaponics
A place to discuss aquaponics

I don't think there really is an acceptable level. Different types of fish are more or less sensitive and age makes a difference as well. You do occasionally see traces but this conversion takes place fast enough that you rarely see any, it's quickly converted to nitrate. If you've salted that helps with the effects on the fish so you can run with a bit of nitrites but backing off or not feeding is a good idea in my opinion.

I didn't feed for 24 hours and nitrites fall to 0,1. Seems good right?

I will add sea salt tomorrow when I will be in town.

What about water hardness GH 12 and KH 4. Is there any number that is optimal? My ph is now 7,8.

One month later, the system is working nicely. Carps are growing and plants as well.

I have indicators of nutrients deficiency I think so on my cucumber plants. Any Idea what it could be?
Ph is 7,7 - 8,0

Some photos of progress:

Seppeo posted a link to a really useful PDF here: viewtopic.php?f=3&t=27463&view=unread#p538950

Going by that, I'd say your plants need potassium. It's not locked out at your pH (Charlie posted a chart here: viewtopic.php?f=45&t=16035&p=391931&hilit=nutrient+lockout+chart#p391931 ) so you can add it by putting a little liquid fertiliser in your water. (Pick one that shows you the N-P-K ratio and doesn't have nitrogen, or you'll spike your ammonia/nitrite levels!)

You could also spray apply the potassium by using seaweed extract (most have about 1 or 2%) or potassium bicarbonate.

Great pdf, I agree that this should be a K deficiency.

I added one cup of seaweed extract to water yesterday.

You think it is better to add it via leaves?

I have roughly 600-700 liters of water. How much and how often can I add the seaweed extract?

There are no NPK numbers on the bottle.

or sulphate of potash which is very common in gardening, horticulture and agriculture.
but you will probably find that you need a small dose of all major trace elements
(this is where the nitrogen/phosphorous free seaweed extracts are beneficial)


pretty much everything should be used in small amounts and best to apply either foliar or with a watering can directly onto the grow beds. My own preference is not to add anything to the fish tanks.
Just water with a watering can onto the media and plants. Then fill up watering can and water with fish tank water to get it into the media near the roots.

you really only need a small watering can to do this (10L or so).

be very careful - you definitely don't want to be adding anything nitrogen based as young systems can spike very easily.
Read the labels of your products carefully looking for N or P - you don't want these.

[edit] when mixing start off using much less dose than what the instructions say.
best to do small amounts regularly (ie. weekly) rather than a lot at once.

Applying it either way is OK and sometimes I'll add to the sump or grow beds but Potassium competes with other ions for uptake when you add it to the system water and over application to the system water may have some effect on the fish so I prefer to spray apply it. It also takes less to get the same benefit so since you've already done the addition to the system water, I'd just spray apply for awhile.

Look on the bottle of seaweed extract, a lot of times they'll give you the amount for a foliar application. I only use it when I see that the plants have a potassium deficiency - about once a week or every two weeks until the deficiency is taken care of. Adding an initial dose to the water is fine and then follow with spray application.

1oz per gallon or 30mls per 3.8 L is the dose for spray application if you can't find it on the bottle will probably work.

I have been adding it to the sump tank without any problems. So this should work.

Will spray it as well, on the bottle is says 10 ml per liter which is almost the same as you said.

When is the best time for spraying? It is mid day now with around 30 celsious / 86F
How often should I spray?

I'd probably spray apply this in the morning but for certain give it enough time for the leaves to dry before nightfall so that you aren't encouraging diseases.

Some things are done at different times of the day for other reasons (like magnesium sulfate) but usually making sure the leaves are dry overnight is a good idea .

It is about time that I tell you some updates about my system.

Have to say that it is doing fine. The growth rate of plants and fishes are amazing.

Plants are consuming all the nitrates so it happens that I feed the fish even 5 times per day, but still usually 3 times.

Levels are:

Ammonia: 0,2
Nitrites: 0
Nitrates: 2
PH: 7,2
Temperature: 24 cellsious

I recently added a swirl filter, and had one fish die: LINK

I am also actively thinking of adding a NFT and DWC and I think this will be done in one month.

I ll post a few photos as they tell more than words