Established Tank But New Fish Dying

A friend no longer wanted her 40 gallon saltwater tank, so I brought it home along with about 15 g of water, a lot of live rock (I didn't weigh it), a large clownfish, small 3 stripe damsel, cleaner shrimp and what I think was a goby. The filter hadn't run for a few days because of a power outage. The tank was quite dirty, so I cleaned it and changed all the filter media (Fluval 305). I used the sand, water, and rock from the old setup. The nitrates were through the roof, so I did a lot of additional vacuuming (moving the rock around even) and water changes. During one of those water changes, the goby died. I don't know if it was from the water quality or trauma from the drastic cleaning. I added several tiny hermit crabs and some turbo snail. Things were chugging along nicely for a week so I added two blue damsels. The first was dead within 48 hours and the second within 72. The main symptom was perpetually open mouth but no gasping at the surface etc.

My water specs are as follows specific gravity 1.019, KH 120, Ph 7.5-8.0, ammonia 0, nitrites 0, nitrates 80 (high I know).

Two questions. How often and how much should I be doing water changes to get the nitrates down? Could high nitrates have killed those fish so quickly? Why are the existing fish not affected? The 3 stripe damsel and clownfish are active and eating well.

 

Hmmm, my first thought was that the cycle was damaged from moving rocks and replacing filter media, but then I read your parameters, and that doesn't appear to be the case. It could be that the goby died from the drastic change to a cleaner tank, and that the damsels didn't adjust well to what is probably a much higher nitrate level than they are used to. It also may be that the difference in salinity did them in. Do you know the salinity of tanks at the fish store? Did you acclimate the damsels very slowly? Your salinity is quite low, and I would slowly raise that level while you bring your nitrates down.

I'd probably go with a water change every 4 days, perhaps 30-40%? Nothing too drastic, but enough to slowly reduce the nitrates so as not to shock your remaining fish. The 3 Stripe and the Clown are both hardy fish, and are likely used to a very dirty tank, so you don't want to make things super clean too fast. It looks like you'll have some work ahead of you, but it will be worth it in the end.

To raise salinity, you may top off with a small amount of saltwater daily. Just a little bit, so this change will also be very slow and stress free on your new little friends.

Unfortunately, you're starting out taking care of someone else's mistakes, but you'll get there. Saltwater is so much fun and we're glad to have you. Welcome to Fishlore!

 

The salinity looks pretty low. Ideally 1.025 is considered the best balance for fish and corals. Fish have a higher tolerance range for salinity than corals but I would personally I would never go below the 1.023 mark for salinity even if I didn't have corals. Are you using tap water or RODI water? Also I noticed you are using the dreaded canister filter which are very prone to being nitrate factories in saltwater aquariums, even when you think you have properly cleaned them out they still have many nooks and crannies where nitrates/nasties can build up. I actually recommend HOB for a tank that size

 

The salinity matches my lfs and I acclimated the damsels out of the tank by slowly adding my water to theirs over an hour. I do use tap water. The damsels were not warmly welcomed by the clown fish and other damsel. Could simple bullying be a cause? The comment about the canister filter made me think I could take a closer look at the ceramics being used. I rinsed them in tank water and changed all the other media, but there could be some goo still hiding in there. Thanks for the ideas!

 

I pulled out the ceramic rings. LOADED with sludge. Gave everything a good rinse with tank water. Let’s see what happens.

 

Tap water is also part of the problem. You can treat it but the fact remains that the minerals in tap water in most areas is prone to promoting nasty algae growth (ie green hair algae). Most recommend using water that has been through a reverse osmosis/de-ionization system (aka RODI system). If you live in an area with a local fish store that does saltwater, chances are they sell RO or RODI/Saltwater pre-mix and that would be better for the tank in the long run. Just an option if you don't want to buy an RODI system.