F8 Extremely lethargic after water change and salinity increase

[savvyvannah]

To whoever can help me,

Summary:
I've had my juvenile F8 for several months now and excepting one issue with an ammonia spike a few months ago, he's been perfectly content and healthy. This morning he seemed a little slower than usual but still interested in food and ate well (brine shrimp). This afternoon, however, he has declined exponentially. The current is pushing him around (I've changed the direction of the filter to stop this to keep him from having to expend too much energy fighting it) and he is now mostly just sitting near the sand on the bottom of the tank. He seems to be having a hard time maintaining his position in the water and every now and then does a headstand. When he does move, it's very weak and he has trouble navigating objects in the tank. He responds to movement within the tank and will swim away if I attempt to nudge him with the net (he was stuck in a plastic plant earlier). His body is also free of any injuries or apparent illness. I am very worried for him.

Diet: He is fed a mixture of frozen brine shrimp, bloodworms, and daphnia. I haven't had any snails small enough to feed him in the last couple of weeks so that is the only thing he's missing truly. His teeth do not appear overgrown.

Water Quality:
pH:6.5
GH: 180ppm (This seems way too high--I'm not sure how to decrease the hardness without hurting him)
KH: 0ppm
NO2: 0ppm
NO3: 20ppm
Ammonia: <0.25ppm (API liquid test; all other parameters were measured with API test strips)
temp: 80°F
SG: In the last month, I added enough marine salt to create an environment with a SG=1.004. Yesterday, I completed a water change and now the SG=1.006. It is my understanding that F8 puffers can withstand a SG change within 0.002. Please let me know if this is not correct.

Tank Setup:
5 gallons
three plastic plants
faux driftwood
sand substrate
Cascade 300 internal canister filter
Aqueon Heater

Tank Mates:
none

Additional info: Each time I do a water change I add Fluval Cycle Concentrated Biological Booster.

Please help!
Savannah

[Pufferpunk]

5g isn't nearly large enough for this species, 15-20 is recommended. Although, I don't believe this is causing his problem. Is it possible he swallowed air? Can he upright himself at all?

No need to add extra bacteria "booster" to an already cycled tank. Especially if the tank is BW, as that bacteria is for FW & will probably just die at that SG, causing more problems. Don't raise the SG any higher. 1.003-5 is fine.

[savvyvannah]

He passed away shortly after my original post. I realize he needed a bigger tank and I was working on a 30g for him. I don't think he had an opportunity to swallow any air and did not appear to be bloated at all. I would love to get to the bottom of this before trying again with another puffer.

I think I may have done too much of a water change. Because of the relative "newness" of my tank, I had some brown algae/diatoms beginning to take over. Instead of my usual 5% water change, I did a 75% water change and cleaned the diatoms from the glass and decor. I wonder if I somehow caused shock to him during this process? If so, why would it take a day and a half for his symptoms to occur? As I said before, he was swimming normally and ate his breakfast that morning and less than six hours later he was gone. I don't believe it was the food either because the brine shrimp I fed him was from the same cube of brine shrimp I had fed him the day before. To be clear, I did remove him from the tank and put him in a holding tank while I was cleaning. The holding tank contained water from his tank that had been siphoned out.

Please help me understand so that I will not repeat any mistakes!

Cheers,
Savannah

[Pufferpunk]

If you usually do 5% (50% weekly is recommended but in a tank that small, I'd have done them 3x/week or more), then 75% definitely would have been a shock to his system. But since you said this was days ago, I'm not too sure that is the specific issue. More so, you possible disturbed the biological filtration & ammonia/nitrite developed. You tested his water while this was happening??

[savvyvannah]

I didn't test the water for a baseline prior to changing the water, but I did testing once I noticed his abnormal behavior. The parameters listed above were what I came up with. I have had an issue with ammonia in the past and he acted in an entirely different way (very erratic) so I'm inclined to think this was not the problem here. This is further supported by testing. I wondered about pH and GH? I know the addition of marine salts changes water chemistry. The water change was the day before he passed away.

[Pufferpunk]

Then it very well may have been a shock to his system, if you did such a large WC when he was used to the water he was in. I often do 75-90% WC but as long as it's done weekly, it's fine. My tank water greatly resembles my tap water.