Backyard Aquaponics
A place to discuss aquaponics

My fishless system has started producing a lot of fruit recently (cucumber, tomato, capsicum) and suddenly slowed. All my research pointed to a potassium deficiency, see photos https://imgur.com/a/OzLJb5g

To solve, based on some napkin maths I added 50g of potassium sulphate to my system of ~1200L. I checked after 2h and my system has gone from ph ~6.7 to about 8.5. Should I let it sort itself out or add something like hydrochloric acid?

Given that its fishless I guess you could try the hydrochloric acid, if there were fish involved I would suggest doing everything gradually and cautiosly, but it might well have been too late anyway! 6.7 was pretty perfect for the plants I guess. Potassium carbonate is used by people here to up their pH, so if you just want to up potassium I think there are other options which wont affect pH as much; potassium bicarbonate, I think... and things like seaweed extract, or simply high potassium liquid fertilizers.

Someone with more hydro experience should be able to give you more advice, most people here are restricted to a handfull of options which aren't harmful to the fish.

I'm reasonably new to this so would like to make mistakes when no fish are at risk, slightly reckless with the quick ph change, however I'd calculated closer to 7.5 not 8.5!

AND



So which is it, Potassium sulphate or Potassium carbonate???

I often tip in 100g of K2CO3 on a daily basis, and the pH remains near 6, when I have a couple of hundred trout in there, total volume 12-13000l.

Oh sorry, K2CO3, Potassium carbonate is what I added. I was reading about potassium sulphate earlier as a good option for those wanting to increase potassium without increasing PH.

I assume with a few hundred trout you'd be dealing with a much larger amount of acidification from the ammonia than my system which is a 10th the size and no fish! What are you growing?

Either way, I've started adding small (<3ml) doses of HCL to bring the ph back to a sensible level. My take-away from this is to do things more slowly in future.

In my large system I'm currently growing all sorts of things, I harvested 12kg of spuds from one GB a few days ago, zucchinis, strawberries, capsicums, asparagus, pumpkins, rhubarb, celery, grapes, gourds. Plenty of pics in that thread, and I'll post some more once I get around to reducing some phone photos to an allowable size to post.

Ah right, yes I read through your post a while back. I have a similar space and eventually plan on something of the same scale down the track. I've always been drawn to the floating raft designs though.

I don't see any symptoms of Potassium deficiency in the pics provided. I would suggest there is a Calcium deficiency, as well as possibly Magnesium and Iron.

Potassium deficiency shows on the oldest leaves of the plant, starting with yellowing around the margins of the leaves, which creeps in toward the centre of the leaf as the deficiency worsens. The yellowing in most cases is solid, not interveinal or giving a mosaic appearance. In sever cases, the yellow outside edges of the leaves start turning necrotic and browning off, giving a burnt look.

When you say "Fishless", how are the plants getting nutrients?... Is this a hydroponic system, or a young aquaponic system you are fishless cycling?

Thanks for checking the photos. After researching for a few months, I finally built the system in October with the intent of adding trout in Feb after learning the ins and outs over summer (I'm in Melbourne).

Part of the fishless plan is so I force myself to learn the input/output balance before subjecting fish to my inexperience. I'm manually adding ~10ml of aqueous ammonia (25%) each week to build nitrates keeping it at about 50ppm, up until december I was adding 50ml of Seasol each week, I've only restarted the seasol after I started this thread when the interveinal chlorosis started appearing. I also add 100ml of worm wee each week just for kicks.

I have some sea shells I can crush up for calcium, liquid iron is easy and epsom salts should deal with the magnesium.

I added a photo of the system from 1 month ago (everything is about 3x bigger now). This is a test system before rolling out something larger in our country property.

I use crushed dolomite for Ca + Mg, plus it helps a bit with raising the pH.


Also, please don't quote the entire previous post, its just up there^^^^^^ if you need to read it again

Use reply instead of quote, it makes it much easier for those trying to read new posts.

Thanks for the advice, I added the following two days ago and the fruit has already started growing again.

Seasol Iron Chelate Magnesium Sulphate Potassium Sulphate
30g 43g 11g 50g

@ kusumanassim Awesome news! Off hand do you know what the total water volume in your system is?

Sorry for the slow reply, I wanted to give the system a couple of weeks to react before replying with results.

The system is a 2 bed IBC CHIFT PIST, so between 1000-1100L.

I've been adding Seasol, Iron Chelate, Magnesium Sulphate & Potassium Sulphate according to the table below every ~7 days. The interveinal chlorosis has improved slightly however it's still present, leaf browning has increased. Fruit production has improved but is well below what i'd expect from a nutrient rich system. I'm keeping Nitrates at about 80-120ppm.

Any ideas?

https://imgur.com/a/Lmn6oPC

Days since last - PH Seasol - Iron Chelate - Magnesium Sulphate - Potassium Sulphate
21/01/2020 - 0 - 7.0 - 30g - 43g - 11g - 50g
27/01/2020 - 6 - 7.0 - 30g - 43g - 11g - 50g
04/02/2020 - 8 - 6.9 - 30g - 43g - 11g - 50g

Thanks for the reply.

This may sound a bit stupid, but I would personally add some goldfish to the fishless cycle or better mosquito fish (from the drains/rivers around melb. that deminish the diversity of local waterways and are easy to id with there spot). I've personnally always found it hard to replicate the services of nature, without employing nature in that service. Symbiosis on all levels is my aim.

Plus I am lazy so all the technical stuff floats over my head before I get it. I've only ever added fish food and shell grit as a buffer in my smaller systems.

To help quell your concerns regarding the quality of life for the fish under your care. Most ponds or aquaiums I regularly see are in such a bad state, the conditions in your AP setup would be a dream life for them. One restaurant in particular spings to mind. Lets just say I didn't order the fish from the menu.

Maybe you're right, I'll add a goldfish later today and if he's alive in a few days I'll add some brook trout. I'll report back once I see a change.