Reverse Osmosis Deionised Water System



I hope as you read you're safe and well. Yesterday afternoon I popped my head into my 12 year old daughters lounge. I was shocked to see her aquarium was on the brink of an algal bloom. I say shocked because she carries out two fifty percent water changes every week. She has a 260 Litre (68 US Gallons / 60 UK Gallons) tank. If I may please, hasten to add, that in order for her to be able to carry out this mammoth task I have set up an semi-automatic system which means she has only to turn a few valves to both empty and fill her tank. Also I didn't want her first footsteps into the world of fish-keeping to be one of "chores". We checked the water parameters and I couldn't believe what they were. The nitrates were 20ppm and the phosphate levels were off the chart, so exceeded 1.8 ppm. I couldn't work out how they had become so poor. We did a 65% water change immediately. We also removed all the rocks and the "contaminated" sand at the front of the tank and left them in a mild bleach overnight. I cleaned all the glass sides of the tank. We finished at 10pm. Today we have carried out 2 more 65% water changes. I've not replaced the rocks or the sand [just] yet, albeit I have rinsed them thoroughly to ensure no bleach residue exists.

Upon completion of the water changes we tested the water again. No difference. Then the penny dropped. We tested our tap water and it was 10ppm nitrates and (as the tank test) this was off the scale for phosphates so exceeding 1.8ppm.

When we first set up the tank we tested our tap water and it was 1ppm nitrates and 0.1ppm phosphates. Neither of which caused any concern. However, and quite naively I have assumed these levels would be a constant. And we all know that assumption is of course the mother of mistake .

We've left the lights off today and nudged the Co2 up just slightly. If I have understood the internet correctly low Co2 helps algae? The algae we are dealing with is a green hair algae and had grown to lengths of about 3 to 5cm. There was also an amount of cyanobacteria (green slime) and I've removed all of that too.

I'm in no doubt that the underlying problem is our tap water. I'm also convinced that we can cope with the nitrate levels and even reduce them as we have used a specific media that provides a full cycle. When it was first used we saw our nitrate levels fall from about 10 to 1ppm. Apart from turning the light off I've no other "immediate" control over the algal/cyanobacteria growth. However, her aquarium is heavily planted and she has an LED light which enhances plant growth (Fluval Plant 3) so turning the light off does feel counter productive in the long term.

Which brings me to the reason for this post. I think the most viable option available is RO(DI) water. Hopefully I have reached the right conclusion. There probably isn't sufficient space under her aquarium to have an RO unit and storage. (Please see photograph) And it's not something we want to have on display in her room. We do have an option to put it in the garage which fortuitously is on the other side of the aquarium. I was hoping to set something up that is no more complicated than the current water change system I have set up for her.

I envisage putting the RO unit on a timer (please correct me if I don't understand this option) and sending the clean water to a storage vessel and was thinking "water butt" or the like? Then having a pond pump in the water butt which could be turned on to fill the fish tank (which in theory would be delivered through a permanent delivery system installed through the wall). I [think] I would like to explore if I can automate the entire process so that a pump in the tank empties say 7.5% of water per day and the tank is topped up automatically with RO water. Is the latter getting into serious expense?

I'm genuinely hopeful there is someone who can perhaps throw some thoughts and advice on this for me please. Thank you

AiYn'U (Asleep in Yorkshire near Hull (pronounced 'Ull)


As far as the ROdi system is concerned, the only problem i see is having to remineralize the water if it is too clean... that mostly depends on the fish species.
The more automation you want, the more expensive it will be. You could always wire an outlet to a "light" switch for pumps so all you have to do is turn them on/off, or use some fish light timers to plug them into to automate the process. They do have the proper pre built systems that do exactly that tho.
Low CO2 doesnt help algae as much as it doesn't let plants out compete it. Things like breaking up the light cycle and adding CO2 or phosphate free ferts will help the plants out compete the algae.

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