expert advice needed, high ALK purple tang life in danger!


New member
Good evening, I need some advice! safest way to lower ALK... purple tang dying :(
Tank background - Elos 120XL, tank volume inc sump around 530 litres. set up 2.5 years ago, pretty much fish only with one soft coral. Running an elos skimmer, cheato & pellet reactor (only been in just under a week).
water measurements today -
salinity 1.024, Mg 950, Calcium 480.. ** ALK 13.5**, nitrates 1

I have an Apex and I have noticed ph doing funny things since Sunday. The cause.. few possibilities.
I had a V2 pure pellet reactor, not done any maintenace on it for over a yr. it appears to be just turning over water, i.e no pellets moving inside. I took it out to clean & bought new pellets. But there was a sludgy mess of pellets at the top of the reactor. so it probably was doing something... i noticed more brown cobweb type algae on rocks after. ph started doing a few funny things. then i decide that salinity was a bit low at 1.0225 (apex said no fluctuation, but I thought due to snail deaths i would try to raise it). So I added about 20l 1.025 salt to my RO reservoir, to gradually increase it. Since Sunday the salinity has increased to now 1.024. The salt water has all been used. Not sure if that could have caused ALK to increase.
my RO I get from "spotless water", have done for about a year.

Now my purple tang has whitespot (a salt like covering over whole body and fins) for 24 hours. My fox face appetite is reducing and i noticed a couple of spots on him tonight. Purple tang is breathing rapidly. I have no way to set up QT.

I have arriving tomorrow from Charterhouse aquatics an Eheim UV steriliser ( I know its a bit late but thought it might help recondition water etc & good for long term)... and Polylab medic white spot treatment? according to them it is reef safe and can help treat white spot? and various different foods.

any other advice? i thought about doing some water changes. someone suggested adding vinegar ? any help would be amazing thank you in advance.

do you think the purple tang will fight it off? they are all very fat healthy fully grown fish before.


New member
No. All of the fish in the DT will die within a week or so (and more likely, within the next 3 days) if you don't pull them out and put them in QT. They have an infection of cryptocaryon irritans that has nothing to do with the alkalinity or the biopellet reactor.

I don't mean to be harsh with this statement, but many of us that help out beginners see it over, and over and over again. You cannot successfully keep saltwater fish without quarantining them. Period.

Edit: By the way, you could choose to sacrifice the coral and any other inverts in the tank by rapidly lowering the specific gravity to 1.015 tonight (and I do mean tonight!), and further lowering it to 1.009 tomorrow. This will do two things - it will interrupt the life cycle of cryptocaryon irritans so that additional theronts don't attach to the fish (and especially, the fishes' gills), and it will greatly assist the fish in getting oxygen. They're deprived of this at the moment, because cryptocaryon preferentially infects gill tissue.

Doing this may cause a massive die-off of small inverts in the tank if there's a lot of them in liverock, which could result in a large ammonia spike, which will also kill the fish. So you'll need to be ready with large water changes, and some Amquel to reduce the toxicity of the ammonia. Note also that you must have an accurate refractometer to accomplish this hyposalinity treatment. Anything less than 1.009 will also seriously stress the fish.
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Premium Member
I agree that alkalinity at 13.5 is perfectly safe for fish. People ran tanks at 18 dKH or so for longer periods, back a long time ago. Vinegar will reduce alkalinity only very temporarily. As bacteria consume the organic acid, the alkalinity will rise back up.

I agree with treating the disease with a quarantine tank. That might be marine ich, which can be treated in a few different ways. A picture might help with a diagnosis, but I'd get a quarantine tank set up as quickly as possible. The filtration is going to be the problem. Running a sponge filter or the like on your main tank for a bit might help seed a new filter.