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Backyard pond system looking to become decoupled

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Last year I converted a 1500l pond in my backyard to an aquaponic system by adding a 3sqm clay pebble media bed next to it.  An 8000lph pump is connected to a y fitting of which one branch goes to the media bed and other branch to an pressure filter , both branches draining back into the pond obviously in a closed loop.   The reason for that branching rather than serially connecting the filter and media bed is purely because it required less pipe work as the  existing filter was located near a waterfall on the other side of the pond and for esthetic reasons allowing pipe to be hidden better.  I disconnected the waterfall as it contains mortar raising the ph

Ive had pretty good growth this year yielding 80 lettuce heads in the beginning of the season and hundreds of tomatoes from from 6 plants that took over the media bed, courgettes, mint etc. .(I supplemented potassium and phosphates). I'm really pleased, however high ph is a real problem which I'm always fighting  

My tap water is very hard at ph 8.5, so I treat my top up water to 6.5 in a 210l rainbutt. I manage to keep my pond ph stable around 7.5 like that. I use phosphoric acid as phosphates buffer around 7 , but when phosphates are a bit high I switch to hydrochloric acid.  I have no issue with algae. My pond is surrounded by patio stones with mortar and a mortar and stone waterfall I decommissioned  for ph reasons, but when it rains it leaches carbonates into my pond which of course is another source of ph increases. 

My system works but I was wondering if I can do better than having to actively lower ph of a 1500l body of water all the time. I've got the discipline down and havent killed fish in months, but I was wondering if I should accept the fish pond wants to be ph 8.5 and go decoupled. 

Im not quite sure how to approach it the best way , there is very little I can find online that doesn't get above my head.     I've done an experiment where i built a DWC rack with 40 lettuce with 35l nutrient reservoir which I manually supply with ph treated water from a 100l mineralisation tank I  routinely fill with backwash from my pressure filter. Results are not great so far. Lettuce is growing but very slow. This could be because of the late season in the UK, my dwc build not very good , not enough sunlight or maybe the quality of the nutrients from my mineralisation tank. I can detect nitrates. Maybe I don't change the reservoir water enough.   

Lots of variables here, so I came to ask for help and advice. 

How do I approach decoupled ? What are my options. I want minimum maintenance as possible.  Even open for auto dosing ph on my plant side system  

Here are some pictures  of the system





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There are many options for this.   The simplest and least maintenance option would be to use a wicking bed and water with backwash and water changes from your pond.  With a wicking bed you can supplement if needed without concern for the fish.   I did this with my first incarnation of a greenwater system that due to the algae ran very high pH as well.  The wicking bed offset the pH and grew relatively well as compared to gravel beds I was trialing by running the water through them.   You will also need less equipment as you wont have to have a pump. Though it will require a method of filling.   A five gallon bucket will work for small bed like a 8ft x 4 ft bed.  A larger bed might be less back breaking with a pump.


There are mortar sealants that might help your pH leaking as well as extend the life of your waterfall.  The calcium being leached is likely weakening the mortar and may lead to cracking over time.   Pond armor is one I've seen that is fish safe.  Just have to be careful to make sure you don't use one that has harmful chemicals.   I don't know if emptying the pond and sealing is possible or practical for you, just putting that out there as a possibility.

Edited by Ravnis (see edit history)

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