Algae Growth on Rockwool Medium

by Phil
(San Diego, Ca)

How to cure algae growth on rockwool?

Answer: Phil- Unfortunately, prevention is the best answer for dealing with algae. Once you have algae, you constantly have small amounts of dying algae. When bits of algae die, microscopic fungi move in and begin to decompose them. The fungi attract fungus gnats, which will make a home in your roots and chew tiny holes in your roots. The tiny holes, of course, let in any pathogen that may be floating by in the water (there are ALWAYS a small amount of pathogens in the water normally).

These pathogens include pythium, wilt, and fusarium....any one of which could wipe out an entire garden pretty quick. In addition to all of this, the algae competes with the roots of your plants for nutrients!

Algae will grow anywhere it finds these three things- water, nutrients, and light. Since the whole hydroponic system is filled with constantly re-circulating nutrient solution, the only one of these three ingredients you are able to remove from the equation is light. Any place in the system where nutrient solution exists, you need to exclude light as much as possible. Keep your nutrient solution in a light-proof reservoir (with a lid). Make sure there is not light exposure where the nutrient solution enters the system and where it returns to the reservoir. For drip system, you can cover the tops of your planting medium with pieces of black plastic, with the drip emitters run underneath the plastic. Keeping the light off the rockwool will prevent algae growth on the rockwool.

Once you have algae in your system, you don't have very many options. Anything that kills the algae will almost certainly lead to fungus gnats. That said, you can still light-proof the system as much as possible. You can also add a small amount of Hydrogen Peroxide into the nutrient reservoir. Once you begin killing back the algae, you MAY want to change the nutrient solution more frequently (as it will become saturated with bits of dead algae). Be sure to read my page on using Hydrogen Peroxide if you decide to go this route, as the Peroxide can wipe out your entire garden just as quickly as pythium or fusarium if you use it improperly. I sure hope this helps you out Phil, and Happy Growing!

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(10 week update below)

Find out the cheapest and easiest ways to garden productively in this article.

Hi everyone, Jason from Jason's Indoor Guide here. When I got started with hydroponic gardening more than 24 years ago, my first garden used rockwool cubes and B.C. Nutrients....and I remember thinking to myself yeah, sure, there may be a lot of advantages to gardening with hydroponics, for example there are very few pest problems, therefore very little pest control, no weeding, no plowing or tilling the soil, no soil testing or having to add things into the garden soil, no watering the garden....but for someone who just wants to grow their own vegetables and have more control over their food supply and the quality of the food that they eat, the cost of constantly having to buy grow media and hydroponic nutrients makes this an expensive hobby for most people...

Epic Nutrient Change

I suppose when you take into consideration how much money you save NOT having to buy food at the grocery store, it is surely cheaper to grow your own food hydroponically even with the cost of high quality nutrients. Nevertheless, I didn't have a whole lot of money to work with and I needed to make my efforts as affordable and effective as possible....and in the last 24 years I HAVE learned a thing or two!

As you browse through Jason's Indoor Guide, you will notice all of the systems that I use personally are homemade systems. As I got 3 or 4 years of experience under my belt, I quickly adopted a preference to standing water systems and systems that use expanded clay pellets or lava rock, because the media is re-usable and it eliminates a huge operating expense. So once a hydroponic system is built, garden maintenance is minimal- check and adjust the nutrient solution daily, and to change it completely every 2 weeks....and the biggest operating cost is the hydroponic nutrients. (and the electric bill, lol)...

Homemade Cloner

And, regarding the cost of the nutrients....I experimented for about 3 years with making different compost teas and nutrient teas, but there is still a lot of expense $$$ associated with making high quality nutrient kelp meal, liquid seaweed, rock dust, bat guano, un-Sulfured molasses, worm castings. You can eliminate a lot of this expense by becoming an expert at making high-quality colloidal humus compost, and use your properly made compost as the basis of your hydroponic nutrient solution.

Unfortunately, I have been gardening for over 24 years and I have only just recently mastered this difficult skill....and even then, only because I happened to find a very easy to follow, high quality technique and decided to follow the instructions to the letter. I produced more high quality compost in just one week than I was able to use in a whole year! If you can master the technique, I highly recommend it. It is one of the top 3 things you can do to increase the productivity of your food production efforts, while at the same time decreasing the amount of effort required to grow all of your own food, and decreasing the total cost of operating your food production system.

And when I say decrease operating costs, I mean decrease them to almost ZERO, especially if you are producing your own nutrients...

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The ultimate solution to eliminate the cost of your hydroponic nutrients: Imagine a hydroponic system that does not require you to buy any nutrients, does not require you to make your own compost, and does not require you to brew your own nutrient tea. Seriously! No cost and no effort as far as providing nutrients to your plants! Plus, at the end of the gardening cycle you harvest all of your garden vegetables, PLUS YOU HARVEST FISH from the system--->


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This solution is aquaponics. If you are serious about producing all of your own food and being self-sufficient, this is the ultimate solution for reducing expenses (as much as possible), reducing the total amount of work required, and maximizing the productivity of your gardening efforts. I have been gardening for over 24 years, and it is the perfect food production solution in my opinion.

Produce garnden vegetables AND fish together. Eliminate fertilizer costs!

Besides mastering how to make high quality compost, learning aquaponics is one of the top 3 things you can do to increase your garden productivity, reduce your total costs, and reduce your total work. The product that I learned from is called Aquaponics4you. With all of my hydroponic gardening experience, the first time I came across the Aquaponics4you product I knew immediately that it was something very special! Place an aquaponics system outdoors and use the sun instead of grow lights, and you have reduced every garden expense to nearly ZERO!

The Same System/ 10 Weeks Later!

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