Potassium Silicate & Calcium Carbonate A Better Way to pH

For a long time you have been told potassium hydroxide and calcium hydroxide are the go to pH up minerals for pH up. While this does change the pH efficiently it doesn’t provide much benefit to the plants. This thinking was based on old hydroponic chemistry mostly based around chemistry models that had nothing to do with growing anything at all and more to do with just changing the pH. While it does accomplish the goal there are far more beneficial ways to adjust pH for aquaponics.

The much better way to adjust your pH is by alternating Potassium Silicate and Calcium Carbonate which both provide 2 benefits to your plants instead of one.

Potassium Silicate increases your silica levels which are almost universally deficient in aquaponic systems. Silica should be maintained above 60 ppms to ensure proper plant health and disease resistance in aquaponics. When above this threshold it dramatically increases disease resistance, increase crispness and longer storage time by as much as 7 days, reduce heat and cold stress including longer time to bolt on lettuce, and improved system health. It also adds additional potassium as well while raising pH similarly to other options. Potassium bicarbonate can also be used in a pinch to further boost alkalinity when needed.

Calcium Carbonate adds calcium and carbon to the water increasing your calcium and helping your microbes replicate far better than hydroxide. If you alkalinity (dissolved carbonate) gets to low is slows down microbial replication hamstringing your system.

This is why hydroxides while great for chemistry are a poor choice for aquaponics. By switching your pH up combo you can improve system health dramatically while reducing monthly costs on a range of related expenses.


Good post Steve I agree almost every aquaponic system or hydroponic system I have seen WQ testing for is low in silicon. It should be noted that potassium silicate (unless derived from natural sand) is only approved for foliar applications in organic operations and it not approved for adding directly to the water.

Often most of the Aquaponic farms I have been to and seen don’t worry about organic certifications because they can get equivalent pricing in their local communities in which case adding directly to your system water it is a great way to boost pH get silica and potassium


Yes for organic certified you have to use Silicone Dioxide which is OMRI available via Montana Grow or a few other suppliers as well.

Organic Certification for most markets is a self imposed tax and increase in production cost for a tiny gain in profits. When you count up the cost of labor for paperwork, increase facility costs, cost of implementation and equipment its almost always over 35,000 a year for most commercial farms and that just isn’t made up on the back end when most crops aren’t that much more these days for organic given the increased production commercially now of organic certified products. For most customers your far better off ignoring organic and branding around aquaponics and not overly restricting yourself for a loss at the end of the year in most cases. Organic just isn’t reasonable to many regulations that don’t have anything to do with food safety at all its mostly now used to gate small producers from the market more than anything else.


Thank you so much. We will shift to the method you recommend. How are you testing silica in your systems?

Hannah makes a great silica test

Thank you so much. We will start measuring silica and I really appreciate your excellent explanation of why it is so important in aquaponics.

Interesting conversation! I have successfully been using Potassium bicarb for many years in conjunction with crushed oyster shells (calcium carbonate) for pH adjustments. They are very reliable, easily sourced and inexpensive. I have never understood the rationale for using hydroxides etc… for pH adjustment in a “living” system when gentler options are available.
I am interested in acquiring more info regarding Potassium Silicate as the only papers I have read about it is for foliar application. Assistance with acquiring more info about dosing and locating companies that ship internationally would be greatly appreciated. Cheers

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Another great example of why we can’t keep just relying solely on universities to move our industry forward its way to slow and its hindering progress of our industry as a whole. Commercial production can provide data that is just as valid.

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I make stinging nettle tea, which has a great source of silica among many other nutrients. I use it as a foliar spray and add in into my systems along with compost teas. They work great for Aquaponics and traditional gardens alike.

Stinging nettle is one of the best plant bio-accumulators you can use for mineral inputs for your plants. It has over 8 times as much available silica as horsetail which is often thought of as a good source. It is also good for nutrient ferments such as plant LABs using stinging nettle and provide even more than tea alone. You can add plants to LABs ferments to provide different beneficial compounds compared to teas. Its a great way to further diversify the nutrients available to you with out adding inputs your not use to.

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I am wondering what kind of precipitates and solids can form in your system if you are adding plant ferments and compost teas? These seem like really great sustainable options, but do they have any drawbacks such as forming biofilms? Is this a commercially viable technique or are purified potassium silicate and calcium carbonate a better source? Thanks

Secondary compounds entirely depends on what input source your using. Avoid anything with saponins for example such as yucca. Some plants are highly beneficial some aren’t some do a great job of boosting certain terpenes some do not. I you want a good resource to start your journey this is a good one. http://cdn.shopify.com/s/files/1/0248/9641/files/Dynamic_Accumulators_and_Nutrient_Contents.xlsx?723
For commercial tho its harder to rely on biodynamic inputs consistency at scale so your better off using potassium silicate and calcium carbonate for commercial but it is entirely possible to use more natural inputs if broken down properly. This is commonly done for soil inputs.

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Thank you so much for this useful information! I look forward to more of your posts!

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I am focusing on growing low potassium lettuce via aquaponics. In case I added potassium silicate how much potassium can be increased in the lettuce. We have to grow the lettuce of max.100mg potassium per 100g of lettuce for the patients of chronic kidney disease

Thank you for your good info
Sam Kay - [email protected]

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You generally want around 60 - 70 ppm of potassium in aquaponics for lettuce.