Silicates affecting plants.

  • #1
My freshwater planted aquarium (240L) has been running for almost 2 years.
Generally, the tank over time has got to a very good condition.
It is very well planted with community fish.
I do regular water changes and use well known testing kits to check the water condition.
The algae in the tank never gets to much as I have algae eating fish which do a good job.
What I do get especially on the plants is a black/ brown algae (not sure if it is algae).
I have removed the affected plants and used bleach to remove the algae. This works and when I use my fingernail
I can scrape it off and it is brown in color.
I did some research, and this could be caused by silicate in our tap water
The testing kits I have do not have silicate testing. After purchasing one the tap water was off the scale
for silicates. I now use a silicate remover in the filter. This does reduce the amount of silicate in the tank but
of cause water changes just add more to the tank water.
I am considering a ro/di system.
My idea is to use ro water just for water changes. The question is do I have to remineralize the ro water before adding to the tank.
The water changes are about 30% weekly. Will the remaining water in the tank be enough to remineralize the added ro water?
Thanks, any suggestions appreciated.
  • #2
I'm a bit surprised by the amount / frequency of water changes, given a quick view of your tank.

I'd probably consider mixing your tap with RO in a certain ratio. The exact ratio depends on the water parameters you target, gH, kH, pH.

If you have determined the preferred ratio, you can calculate the minerals and trace elements that are most likely in your mixed water and optionally change the nutrients you normally add manually.

If your tap water is soft, mixing with RO will only make it softer, so a dedicated additive is likely required.

Going for 100% RO, then yes, you need to re-mineralize the water. The benefit of course is you can create an ideal mix for your planted tank.
  • Thread Starter
  • #3
The water changes are usually around 7 to 10 days.
It's like a lot of things you get so much conflicting suggestions around the subject
that after some trial and error this works for me and the aquarium.
Still working on the RO/DI idea but I am leaning towards a RO/DI system.
I will remineralize the water for the tank.
I am also looking into remineralizing for our own benefit. I am assuming that I would need 2 different
mineral types.
  • #4
If it works for you, it works for you.

Good question whether you need to split those up. Certain treatments can be omitted for both purposes, I assume. Deacidification is a typical procedure, which is not required. Disinfection is not required.

For humans at least, I believe a lot of RO units suppliers offer a mineral filter add-on. Or you can use alternatives, such as "green powder". Ideal mineral contents for humans varies with age; if you go to these lengths anyhow, you might just as well take this into account.

For plants, remineralize with potassium bicarbonate to target around 2 dKH, and calcium sulfate and magnesium sulfate in 3:1 ratio to target around 5 dGH. Values might deviate as long as they are kept rather stable. Next, you need to add the other minerals and trace elements required by plants.

Some of the more fanatic planted tank owners, I believe, simply follow EI dosing after a 100% RO water change. But I think most mix RO with tap.

Hope you have a purpose for the waste water, other than a sink.

...this is my short answer - Im a bit time-limited.
  • Thread Starter
  • #5
Can`t wait for the full answer
We have a large garden.... Say no more.
  • #6
I would consult with experts if you intend to use it for drinking purposes. I don't want to be responsible for someone's premature death ;). And look up "mineralization filters" that are used to turn RO water into drinking water. These might actually be suitable for planted tanks also...

In any case look up the water report from your local water utility company. No doubt you can find the report online, which conveys the contents of your tap water and allows you to derive mineral contents.

If you know the mineral contents and would dilute this water with RO water in a fixed ratio, concentrations drop to give you more preferrable GH and KH measures, along with less silicates. This is the easiest route for most planted tanks and I think adopted by most planted tank enthusiasts. KH in tap water is mostly likely determined by bicarbonates. 1 dKH equals 21,8 mg/l bicarbonates. So look it up and you know a ke parameter.

If the drop is not enough, alter the ratio, so more RO water is used in the mix to further drop the KH and silicate concentrations. Add a GH booster to bring up GH.

Mixing RO water with tap water will also drop the PH, which is likely acidified through CO2 depletion by the water utility company. PH has an effect on nutrient intake by plants, can be a little hard to control. Focus on the related KH and measure PH in your tank and perhaps choose a chelated iron that fits with the PH.

...I'm almost sounding like a high tech planted tank owner. I don't go into all this trouble myself. I do have a RO unit for my blackwater tanks and for a planted tank that has taiwan bee shrimp, which I mineralize with a product specific for taiwan bees. For all my other planted tanks, I simply add my 5.3 dKH, 6.6 dGH and 7.8 PH water, and it's all good.

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