Jump to content
Sign in to follow this  

Hydra Stream

Recommended Posts

Many have heard of the Ocean Free Hydra Depurator - device that generates Hydroxyl (OH) radicals to purify water.

Many are unclear how the technology works despite reading the FAQ & more importantly how it benefits our reef tanks. I’m not affiliated to Qian Hu in any way but would like to share my findings with the reefing community having used this product since Oct 15.

Background reading on chemistry & technology behind the product. http://www.yihufish.com/products/product-information/of-hydra-powered-by-hydro-pure-technology/frequently-asked-questions-faq

Key summary:

  •          Increases ORP (oxidation reduction potential) marginally. This is a good thing
  •         Does not reduce nitrates if already present. Other nutrient export method required (eg. bio pellet/skimmer)
  •         With prolonged use, the system nitrate level reduces slightly
  •         Really does remove toxic ammonia. Great for emergency needs & quarantine tanks (without medication). Able to add livestock within a day.


There were several models of the Hydra available catering from nano tanks to medium sized units with built in pumps. I got the largest model Hydra Stream 3 which needed an external pump to supply water through it.  





These cartridges contain proprietary media (similar to carbon) needs to be inserted 1 by one. Not inserted all at one go like what I tried to do. A very tight fit.



I used the angle adapter. Remember to insert the black o-ring as mentioned in the instructions. The white plumbers tape is not necessary. O ring is sufficient.



It’s recommended to mount it vertically so that the entire chamber is filled with water.



Power consumption of the Hydra stream 3 unit is about 2Watts.





I have an ORP sensor hooked up to the APEX Neptune. For this chart & review, it turned off the Hydra for 1 week. 



More about ORP : http://www.reefkeeping.com/issues/2003-12/rhf/feature/

ORP runs around 250mv to 350mv in the sea.

For my tank, ORP runs in the 280+mv range with the Hydra off. It never crosses the 300 mark for the past months. With the Hydra switched on, it increases marginally to the 317+ range within a couple of hours. It will continue upwards towards the 330 range. This shows that the Hydra is indeed increasing the oxidizing potential.

Most associate ORP measurement with Ozone. Generally, the higher the ORP number, the cleaner the water. The benefits of ozone are well documented – increases oxidizing potential, converts ammonia to nitrate among other ways of purifying the water. However, ozone needs to be handled carefully as the potential health effects associated is dangerous for an inexperienced reefer. Details here -  http://reefkeeping.com/issues/2006-03/rhf/index.php

I got the Hydra because it improves oxidation potential without the risk of Ozone. Over prolonged use, I observe an improvement in water quality & clarity. Googling further, publications that state that hydroxyl radicals react with organic waste until complete mineralization occurs. These are skimmed out easily resulting in improved water clarity. 

It’s documented that higher oxidation levels can lead to lower nitrates, probably via the above mentioned mechanism. (Refer to the earlier link under the section “Oxidation of Organics by Ozone: Skimming and Nutrients”). While they Hydra does not reduce nitrates directly, at a reef system level, lower nitrates is possible. In my case, I’ve seen nitrates coming down from 5ppm to the 2ppm range (pic taken before water change). Note there are also other factors such as feeding habits & reactor tuning as well.



IMO, the effect of the Hydra does not have the punch of an Ozone generator, but in a small way, it does have a small positive impact to water quality.


Does it reduce nitrates?


I ran a simple experiment to see if nitrates can be reduced. Here is the set up :

  • 40L Zoanthid frag tank without any fishes. Simple biological filtration (biohome & filter wool). Water circulates via an Eheim compact 600 pump. Auto water top up with RODI water. Lights come on 6 hours a day.
  • No fishes => no food was added during the week => no new ammonia source added.
  • Initial nitrate level is 50ppm (25 Oct 2015). Hydra switched on 24hrs a day for a week.



Nitrate levels were taken every 2 days. On the 6th day, nitrate levels remained at 50ppm (1st Nov)


Results show it does not convert/reduce existing nitrates already in the system.


Other observations & notes :

·         The claims about converting toxic ammonia to less toxic nitrate is true. I’ve put fishes in an uncycled tank with the Hydra without issues. This equipment is just perfect for quarantine tanks or emergency purposes

·         As the conductive media is made of carbon, it’s not advisable to use it in a hospital or medicated tank. This was also mentioned in the instructions sheet.

·         Proper mechanical filtration (skimmer) is still required. This continues to help prevent excessive organics be converted to nitrates in the first place. They Hydra does not replace a skimmer.

·         Nutrient/nitrate export is still required (eg. Water change, biopellet + skimmer)

·         Did not observe a reduction in skimmate. Still able to get a full cup in 3-5 days.



To round it about the Hydra Stream:

  •          Increases ORP (oxidation reduction potential) marginally. Improves overall water quality
  •           Does not reduce nitrates if already present. Other nutrient export method required (eg biopellet/skimmer)
  •          With prolonged use, the system nitrate level reduces slightly
  •           Great for quarantine tanks & emergency


Edited by SubzeroLT
  • Like 2

Share this post

Link to post
Share on other sites

Thanks for sharing the key takeaways. I enjoy the read

Share this post

Link to post
Share on other sites

i heard that the effect is better using oversized unit of the Hydra and increasing the water flowing through it , anyone got any experience with this ?

Share this post

Link to post
Share on other sites

I understand that the reactions are quite instantaneous inside the chamber & there isn't a need for long contact time (unlike a UV filter). Hence a relatively high flow rate is OK.

The stream 3 is rated for 2500L volumes and i'm using it for a 200L tank. That's way over specified & works well.

Share this post

Link to post
Share on other sites

Nice and detail article ! Thanks for the great info 

Share this post

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

  • Create New...