Parameters excellent seeing signs of green hair algae on rock ?


Reefing newb

ammonia & nitrites 0
nitrates 0.00 elos
phos 0.03 hanna checker
alk 7.8 hanna checker
cal 420 hanna checker
mag 1250 elos
As you can see in the photo I am Seeing the first signs of green hair algae on rocks. Not noticeable to a bystander yet - but to me (i know my tank)
Is there anything I can do to stop an outbreak
I did just replace 4 of the T5 bulbs recently ?
Water changes are approx 250 liters every 3-4 weeks.
Do tank readings every week only ever have to dose ALK and CAL ?
Changed out sand bed about 3 months ago am getting some diatoms (on sand only)
Run a phosban reactor with rowaphos
carbon reactor with Seachem Carbon

Also wondering if tank is stable and parameters are good do you have to do water changes as often or do you just do them when readings start rising ? I do them every 3-4 weeks because I want the fish to have fresh water but the readings all suggest that it may not be necessary. Previous owner of this tank only did them every 3 months ?


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You are probably seeing no excessive nutrients BECAUSE of the hair algae scavenging the free nutrients, so the algae may be keeping the nutrients barely measurable. If the problem is true green hair algae (briopsis sp.) then it can be reduced by elevating your Magnesium to about 1400 to 1450 and keeping it there. I'm not sure of the actual reactions responsible for this, but in nearly 30 years in the Reef hobby I can tell you it works better than anything I have tried.
Most people do a partial water change every week or two and of course topping off daily or every couple days. I suppose if you've been doing monthly and your inhabitants are staying happy, then by all means, don't change anything. However, if you want to solve hair algae, I suggest weekly changes and try cerith and dwarf cerith snails. Never tried raising mag, but I trust Mitch that that's another valid option. I would definitely get those snails, along with astreas, nerites and nassarius if you don't already have those.
Thank you both for all your suggestions, I will up the number of snails we only have about 10 at the moment. I will also try up the mag (currently at 1250). will dosing the mag have any effects on the cal and alk ? Is it still safe for corals and inverts ? I am really new to all this dosing stuff ? Can you recommend a good mag dose product ? We do a 250ltr change each time with is approx 25% of the tank, might do it fortnightly and see if it makes a difference. We have an auto top off and it uses about 25litres every 3 days of rodi !
No, dosing mag allows for the intake of cal. It has no effect on anything else. If interested, a emarld crab is great for hair algae. Sea hairs are awesome too, but must be kept by experts.
I do 2 5g w/c's per week and with the cold weather I usually top off 2g of water a day.
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I hate to argue, but elevated Magnesium does reduce Briopsis sp. as well as several other hair algae. Also, Magnesium is the third leg of a triple relationship between Calcium, Alkalinity and Magnesium. Your levels are high enough to prevent problems with the other two but if you see a tank where the hobbyist is constantly chasing pH and Alk then the Mg is most likely low. A dear friend gives talks about the three pronged nature of the control.

Regarding the interrelationship between Ca, Alk and Mg I can provide direct scientific proof to the role of Mg.

Regarding the role of Magnesium in reducing problem hair algae, all I have is nearly 28 successful years of keeping Scleractins. I feel that is a bit of a credential.